TEMPE, Ariz. -- The Arizona Cardinals, who lost two wide receivers to season-ending injuries in the past two weeks, might be without another one Sunday.

David Boston sat out Wednesday's practice and underwent an MRI exam on his right knee. Boston has been bothered by tendinitis periodically since a mini-camp in Tucson this summer. The problem surfaced again during training camp and in recent days. He was listed as questionable for Sunday's game.

"It's kind of been on and off,'' wide receivers coach Jerry Sullivan said. "I'm not a doctor, but I think he's probably going to have to get something done at the end of the year. It's his patella I think.''

After a breakout Pro Bowl season a year ago, when he led the NFC in yards receiving, Boston has been plagued by dropped passes and a sore right foot throughout this season. He had only one catch, and two drops, in last weekend's 27-14 loss to St. Louis.

Results of the MRI weren't expected until Thursday.

"I don't want to talk about it,'' was all Boston would say.

Arizona lost its two fastest players -- receivers Bryan Gilmore (broken leg) and MarTay Jenkins (fractured shoulder blade) -- in the last two games, losses to San Francisco and St. Louis.

If Boston can't play Sunday, rookie Jason McAddley would join Frank Sanders as the starting wideouts.

"People are going to hurt. This is a physical game,'' McAddley said. "When you have the opportunity, you've got to step up and make plays.''

The third receiver would be Jake Soliday, an undrafted rookie out of Northern Iowa.

The Cardinals signed wide receiver Nathan Poole off the practiced squad to take Jenkins' roster spot.

McAddley, a fifth-round draft pick from Alabama who was inactive the first seven games of the season, made his first two NFL catches last week against St. Louis.

"It's crazy,'' McAddley said. "Two weeks ago I was basically the sixth receiver, sitting on the sidelines. Last week, I was thrown into the fire. It was kind of hectic playing different positions that I wasn't prepared for. But we got through it, and now we've got another week of practice."

Coach Dave McGinnis said he always has been impressed by McAddley's maturity.

"We had it in our mind entirely from training camp on that there was going to come a time this season when he was going to contribute,'' McGinnis said. "It's come sooner than we expected because of the two injuries to our two wide receivers. Now with David possibly being down, it steps it up even more.

"But I've got complete confidence in he and Frank, if they're our starters, and we'll go.''

Jake Plummer didn't throw in practice Wednesday because of a sore shoulder, but he is expected to be ready Sunday.

Center Mike Gruttadauria is questionable because of a sore knee. He also underwent an MRI on Wednesday.

"I don't want to do anything stupid,'' he said, "but I definitely want to be out there to help my team.''

On the positive side, offensive tackle Anthony Clement went through his first full practice since being sidelined with torn triceps in the preseason. Clement could suit up for the game Sunday and be available in an emergency.

"I'll be fine if he at least lets me suit up so I could be available if somebody gets hurt,'' Clement said. "I wasn't looking to play until I had two good weeks of practice.''