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)

Philadelphia Eagles quarterback Carson Wentz underwent a scan on his back Wednesday that was inconclusive and was scheduled to undergo an MRI on Thursday to help diagnose an issue that has plagued him for several weeks, a source told ESPN's Adam Schefter.

Wentz is unlikely to play Sunday night against the Los Angeles Rams, the source said. NFL Network first reported that Wentz was unlikely to play this week.

Eagles coach Doug Pederson said Wednesday that Wentz was experiencing "soreness" and "tightness" in his back and wouldn't practice.

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 Wednesday's absence marked the first time he has missed a practice this season.

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 Los Angeles Memorial 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 Nick Foles will take the reins as the 6-7 Eagles try to keep their playoff hopes alive against the 11-2 Rams.

ESPN's Tim McManus contributed to this report.