Logan Thomas' season is over as the Washington Football Team is placing the tight end on injured reserve Wednesday as doctors continue to figure out the extent of his knee injury, a source told ESPN's Adam Schefter.

This will be Thomas' second time on injured reserve this season and by rule he can't be designated to return again.

Coach Ron Rivera on Monday said that an MRI revealed that Thomas did not tear his ACL, as was originally feared, but that there was damage to his knee.

Washington has won four in a row and currently owns the sixth playoff spot. Thomas already missed six games this season because of a hamstring injury, which landed him on injured reserve the first time.

Thomas was hurt with 10 minutes left in Sunday's 17-15 win over the Las Vegas Raiders when defensive end Yannick Ngakoue went low as Thomas pulled from the opposite side to block him. Rivera said he wishes Ngakoue had used his hands to fight off Thomas rather than go low.

Thomas was a key target for Washington, especially in the red zone, and had developed into a physical blocker. He caught a career-high 72 passes and six touchdowns last season, earning a three-year contract extension worth up to $24.05 million. In parts of six games this season, Thomas caught 18 passes, including three for scores. He leads all NFL tight ends since the start of last season with 151 yards receiving in the red zone. At 6-foot-6, 250 pounds, the former quarterback makes for a big target.

Washington should be helped this week with the expected return of tight end Ricky Seals-Jones, who missed the last three games with a hip injury. It also has rookie John Bates, who has earned praise for his blocking in particular.

ESPN's John Keim contributed to this report.