"He's had it for years, and he disturbed it in the last game, and he thought it would be fine," Reid said. "He came out in Monday practice, Wednesday practice, and it didn't feel right. So back him up and let the thing settle down, and we'll see how he does tomorrow and on Sunday."
The severity of the injury will be something to monitor in coming weeks. The selection of Watkins was immediately under scrutiny because Watkins was 26 and had limited football experience growing up in Canada. The Eagles expected Watkins to emerge in his second season in offensive line coach Howard Mudd's system.
"I won't tell you that his last game was his best game," Reid said on Wednesday. "He had a few games in there that were just top quality games. He just needs to get back to doing what he does. Danny is a good football player. That's why he's here, that's why he was a first-round pick, so you just go play."
With Watkins out of the lineup during practice this week, Reid could have moved either Todd Herremans or King Dunlap from tackle to guard, where they both have played. He instead decided to go with Kelly, a fifth-round draft pick out of Purdue who first practiced at guard during training camp. He had been a tackle.
"We've given Kelly reps. We have trust in him," Reid said. "Rather than moving three guys around, you move one and you go with him."
Sunday will likely be Kelly's first start. His sister already planned on attending the game after visiting their brother Tim, who is a graduate assistant at Penn State.
Kelly is not playing the position he played in college, although teams viewed him as a potential guard during the predraft process because he offers athleticism that most 6-foot-8 players lack and also has size that allows him to withstand interior defensive linemen.
"In a system like this, I think it could work out really well," Kelly said. "It's a lot more aggressive. You get into them, and it kind of takes away their options. You take it to them, and you kind of take out their game plan."
His height would seem to be a deterrence at the position, but Reid pointed out other tall linemen who played guard. The 6-9 Dunlap is an example.
"As long as they can bend," Reid said. "Some of the bigger guys can be stiff in the hips. That's not the case here. He's got good, loose hips. He's able to settle down and play low. As low as you can be when you're that tall."
Eagles fans could become well-acquainted with Kelly, especially if Watkins' injury is more of a concern than initially revealed. Watkins was already struggling; the ankle injury simply provides reason to sit him.
"I think he'll be all right," Reid said. "Let it calm down and see what happens, but I think he'll be fine."
Dennis Kelly File
Position: Right guard.
Drafted: Fifth round (153d overall).
Height, weight: 6-foot-8, 321 pounds.
College experience: Kelly was a captain and two-time team offensive MVP at Purdue, where he played left tackle.
Contact Zach Berman at firstname.lastname@example.org, or follow on Twitter @ZBerm.