Adam Schefter joins SportsCenter to give an injury update on QB Carson Wentz after he didn't practice for the first time this season. (1:21)

The Philadelphia Eagles are concerned that quarterback Carson Wentz won't play on Sunday against the Los Angeles Rams because of a back injury and have told Nick Foles to be ready to play, a source told ESPN's Adam Schefter.

A source told Schefter that the team "will know more later today." Wentz will undergo further testing, sources told ESPN's Chris Mortensen.

Eagles coach Doug Pederson said Wentz would sit out Wednesday's practice with back "soreness" and "tightness" and would not commit to Wentz playing Sunday against the Rams.

"We're going to rest him and continue to evaluate him and make sure he's good," Pederson said.

This isn't the first time this season that Wentz has appeared on the injury report because of his back. He was a limited participant on consecutive Wednesdays in late October, but this marks the first time he has missed a practice this season.

"Sometimes he just gets a little sore, a little tight, and so we're just going to rest him today and evaluate him further," Pederson said.

It was one year ago Monday that Wentz tore the ACL and LCL in his left knee against the Rams. The main storyline heading into this week was Wentz's return to the L.A. Coliseum for the first time since the injury for a rematch against Jared Goff, who went first overall in the 2016 NFL draft, one slot ahead of Wentz.

Now it's unclear if he'll be able to play. If he can't, Super Bowl MVP Foles will take the reins as the 6-7 Eagles try to keep their playoff hopes alive against the 11-2 Rams.

"We're going to focus on today, get through today," Pederson said when asked if there's a chance Wentz will miss this game, "and see where he is at the end of the day."

ESPN's Tim McManus contributed to this report.