UPDATE: According to ESPN, the Patriots fear that Rivers suffered a season-ending knee injury.
Derek Rivers was taking part in a kickoff drill during Wednesday's joint practice with the Texans when he went down with an apparent knee injury. When the rookie third-rounder out of Youngstown State tried to plant and change direction, his left leg seemed to buckle underneath him, and he went down quickly.
After having his leg checked by head trainer Jim Whalen, Rivers walked back to the Greenbrier Sports Performance Center under his own power but with a noticeable limp alongside Whalen and head team physician Dr. Mark Price.
Rivers did not join his teammates on their trip to Houston for Saturday's preseason game. He made his way back to Boston on Wednesday night for further testing. (Offensive tackle LaAdrian Waddle, who did not finish Tuesday's practice at the Greenbrier, also traveled back to Boston on Wednesday.)
The Patriots ask their defensive linemen to wear knee braces, and Rivers had his on at the time of the injury. Bill Belichick has spoken openly in the past about the benefits of having his offensive linemen sport the braces as a preemptive measure.
Rivers had seen time both on the edge and as a stand-up linebacker who floated all over defensive coordinator Matt Patricia's front of late. He could be seen rushing from the outside, dropping into coverage on running backs, or standing over interior offensive linemen during recent practices.
Against the Texans, Rivers flashed an ability to break into the backfield on both days of joint work before his injury. He indicated recently that he was beginning to grasp concepts better and think more quickly in the scheme after arriving to the Patriots as a player who worked almost exclusively as a hand-in-the-dirt left defensive end at Youngstown State.
The Patriots were already without their full contingent of end-of-the-line players before Rivers' injury. Rob Ninkovich announced his retirement early in training camp, and rookie Deatrich Wise left last week's preseason game against the Jaguars with a head injury. Linebacker Shea McClellin, who has experience on the edge, missed both joint practices with the Texans.
Left at the position are Trey Flowers, Kony Ealy, Geneo Grissom and undrafted rookie Caleb Kidder. Lawrence Guy has some positional flexibility, giving the Patriots another potential option, as does undrafted rookie defensive lineman Adam Butler.
Butler took part in 11-on-11 work against the Texans on Wednesday as a stand-up defensive end. He had played primarily defensive tackle -- including spending some time at nose tackle -- this summer, but he said after Wednesday's workout that he had been working on standing up since arriving to New England in the spring. With good quickness and athleticism for his size (6-foot-5, 300 pounds), Butler is an interesting fit on the edge.
Linebacker Harvey Langi has seen a heavy workload on the outside with the top Patriots defense in recent training camp practices. He, along with fellow linebacker Kyle Van Noy, have some versatility to play both off the ball and on the end of the line.
The Patriots signed undrafted rookie Keionta Davis earlier this week, giving them some depth on their defensive front, but he has not yet practiced with Belichick's club. It was discovered at this year's NFL Scouting Combine that the Tennessee-Chattanooga product had a bulging disc in his neck, which likely forced teams to pass on him during the draft.
For about 30 minutes on Wednesday, it looked like the Patriots might be down another edge defender. Ealy went to the turf following an 11-on-11 snap against the Texans and made his way to the sidelines for further evaluation. He eventually returned to the field and had multiple impactful pass-rush snaps during Houston's hurry-up period.
It was the second consecutive day that Ealy showed up positively in terms of pressuring Texans quarterbacks. He was asked following Wednesday's workout what he can focus on in order to continue to build on the positive momentum he seemed to spark in West Virginia.
"Just keep buying in with the team and do what I need to do individually for my preparation," Ealy said.
Though he missed his share on Wednesday, the reps he's received of late have helped his development in the Patriots system, Ealy explained.
"With repetition, you have no choice but to get better," Ealy said. "That's what I feel like I'm doing . . . Despite any (injury) mishaps, we don't want those, but if definitely puts you in a position to see what you're team is built off of when you have shorter numbers.
"I feel like we did what we needed to do under the circumstances, and that gets back to the great coaching that we have and the motivation to push ourselves that we have between each other."
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