Before NFL training camps have begun to kick into high gear, some teams have already felt the sting of the dreaded injury bug.

Many of the players who have been struck down are high-profile stars who are invaluable to their teams. Among them is a three-time NFL Defensive Player of the Year, an unstoppable pass rusher and a couple of outstanding tight ends.

These are the injuries that will have the greatest impact for their respective teams and the NFL as a whole.

J.J. Watt, defensive end, Houston Texans

Replacing the NFL’s most dominant defender won’t be easy. All Watt has managed to do the past five years is win three NFL Defensive Player of the Year awards while racking up 74.5 sacks.

He reportedly could be out for up to 10 weeks after undergoing surgery to repair a herniated disc.

This means the Texans will be looking at even more pressure to perform offensively. The past few years, it’s been Watt and his defensive mates keeping the team afloat while the offense was being led by mediocre passers.

Now free agent acquisitions Brock Osweiler and Lamar Miller will have their chance to prove the team’s commitment to them wasn’t in vain. Should they fail to put points on the board, Houston could be looking at a very slow start out of the gates.

Tyler Eifert, tight end, Cincinnati Bengals

Already without two of his top targets from a year ago in Marvin Jones Mohamed Sanu, quarterback Andy Dalton will likely be without tight end Tyler Eifert to start the season.

Answering a question on the team website about the pass-catching corps, Bengals director of player personnel Duke Tobin made a statement that suggests Eifert won’t be available.

“It’s a position group that’s in flux, and it’s a position group that’s going to have to step up – particularly with Eifert out early in the year.”

Eifert is currently recovering from ankle surgery from an injury suffered in the Pro Bowl, which was originally thought to include a three-month recovery period (more on that here).

Last year was a breakout campaign for the former Notre Dame star. He caught 52 passes for 615 yards and was a beast in the red zone, catching 13 total touchdowns.

If he does miss time early on, then it will be interesting to see how Cincinnati’s offense compensates without him working the seams against linebackers and safeties.

Justin Houston, outside linebacker, Kansas City Chiefs

Justin Houston

The Chiefs are expected to place Houston in the PUP (physically unable to perform) list at the start of training camp, and there is no timetable for his return to action at this time.

“When you’re around him, you have this optimism he’s going to be back in a short period of time, but in reality it’s going to take a little bit,” coach Andy Reid said in mid June, via Adam Teicher of ESPN. “That’s OK. We’ve got other guys that will step in, step up for him at that spot until he gets back. The important thing is that he gets back and is healthy and that you don’t rush it and do something foolish with it.”

Kansas City is smart to take the long view with Houston, who is one of the NFL’s most dominant pure pass rushers.

Despite missing 10 games the past three years, he has racked up 40.5 sacks, six forced fumbles and has even hauled in two interceptions, one of which he returned for a touchdown.

Starting the season without Houston would likely mean more of Dee Ford playing opposite veteran Tamba Hali. That’s not a bad consolation, but he’s not as dynamic in pass-rushing situations or as strong against the run.

Sammy Watkins, wide receiver, Buffalo Bills

It’s expected that Watkins should be ready for the start of the regular season. That’s the good news.

The bad news is that he’s returning from a foot injury, and they are always tricky. Watkins has also been somewhat injury prone thus far in his early career, missing three games last year before breaking his foot this offseason.

Sammy WatkinsAt this point it is not yet known how much Watkins will be able to participate in training camp or when he will take the field at all. However, he told reporters recently that he’s “right where I need to be.”

One reason for optimism is that Watkins looks pretty fast running in a straight line (watch here).

That said, cutting on a dime puts much more pressure on feet that sprinting ahead.

The biggest issue with Watkins is that he hasn’t been able to put in much offseason work in with quarterback Tyrod Taylor. The two had excellent chemistry last year on long passes, but the extended layoff could prove problematic if he is unable to practice with the offense during training camp.

Desmond Bryant, defensive end, Cleveland Browns

Though not in the same class as the top 3-4 defensive ends of the league, Bryant has been a stalwart defender inside for Cleveland since coming over from Oakland in 2013. A long-armed player who defends the run and the pass with acumen, he has tallied 114 tackles and 14.5 sacks for the Browns the past three seasons.

Unfortunately the team will likely be without its starting defensive end for the entire 2016 season after Bryant tore a pectoral muscle working out in mid July. The Browns confirmed he is not expected to play at all this year, though Bryant still maintains hope he can see the field this season.

“Absolutely, I’m hopeful that I can (come back this season),” he said, per Mary Kay Cabot of “The timetable for rehab is 4-6 months, so it’s possible. I’ll do everything I can to get back as soon as I can.”

While Bryant recovers from his injury, Cleveland’s defense will likely need multiple players to step up in his stead. One such athlete who could make a huge difference is rookie Carl Nassib out of Penn State.

Darren McFadden, running back, Dallas Cowboys

Darren McFadden

Fresh off one of the best seasons of his NFL career, McFadden — always injury prone — broke his elbow this offseason and could potentially miss the start of the season while he recovers.

The Cowboys do have a couple of other bruisers at running back to pick up the slack in rookie Ezekiel Elliott (No. 4 overall) and Alfred Morris.

That said, when healthy, there is no doubt McFadden is one of the more explosive running backs in the league. Appearing in all 16 games last year for the Cowboys, he totaled 1,417 yards and three touchdowns, rushing at an impressive clip of 4.6 yards per carry.

McFadden is reportedly getting his elbow scanned and hopes to play this preseason, which would put his recovery ahead of schedule (more on that here).

If he does get healthy enough to play in Week 1, then the Cowboys will have one of the most potent trios of running backs in the NFL. If not, then a lot of pressure will be on the rookie Elliott’s shoulders to succeed right off the bat.

Ian Williams, defensive tackle, San Francisco 49ers

The 49ers have a huge challenge ahead of them this year to keep opposing offenses from running roughshod. Chip Kelly has a history of putting his defenses in harm’s way, thanks to the up-tempo offense he employs.

One of the players who can make a huge difference is Williams, who is extremely stout against the run.

The 49ers actually signed Williams to a five-year extension this spring but ended up making it a one-year deal after he failed to pass a physical stemming from the broken ankle that sidelined him last season.

To this point, there is no timetable for his return and it’s quite possible he could miss the start of the season. Should he be unable to play, then it will likely fall to Mike Purcell to stand in his place on the line at the critical nose tackle position — a huge drop-off in talent that will have significant bearing on how this defense can defend the run.

Jimmy Graham, tight end, Seattle Seahawks

NFL training camp, Jimmy Graham

Largely regarded as the second-best pass-catching tight end in the NFL after Rob Gronkowski before getting traded to the Seahawks, Graham’s tenure in Seattle has been highlighted by ineffectiveness and injury.

Before tearing his patelar tendon last season, Graham was having trouble integrating into Seattle’s run-first offense. He only had 48 catches for 605 yards and just two touchdowns in 11 games.

Chemistry was an issue, meaning any time missed this preseason will only further hurt his case. Head coach Pete Carroll — always optimistic — said he “absolutely” expects Graham to play in Week 1, per John Boyle of the team’s website, but it’s not yet known if he’ll play at all during the preseason.

Making things even more difficult is the fact that Graham’s injury is notoriously difficult to overcome (more on that here).

There is no doubt having Graham contribute in a big way would be a boon for the Seahawks this year. But it’s not a given that he will be able to make that happen.