Cincinnati Bengals rookie quarterback Joe Burrow injured multiple ligaments in his left knee on Sunday, sources told ESPN.

An MRI showed Burrow tore his ACL and MCL and suffered other structural issues, sources said. Bengals coach Zac Taylor would not confirm the extent of the knee damage but said that Burrow will be out for the remainder of the 2020 season.

Taylor did not have a timetable for Burrow's expected surgery or a rough estimate for Burrow's return aside from some point during the 2021 season.

"He's been in great spirits," Taylor said Monday. "On the bus, on the plane, you know, in the facility today, he's responded as well as he could possibly do it and we've all noticed that."

In a tweet Sunday afternoon, Burrow said, "See ya next year," suggesting his 2020 season was done. Cincinnati officially placed this year's top overall draft pick on injured reserve Monday.

Knee injuries of this nature usually sideline players anywhere from nine to 12 months, though each player heals and rehabs differently. But Burrow's status for the start of next season is now in question. Taylor declined to clarify when asked if he believed Burrow will be ready for the start of the 2021 season.

Burrow was carted off the field in the third quarter of Sunday's 20-9 loss at Washington. Burrow suffered the injury after he was sandwiched by two Washington defenders who converged on him on a third-and-2 pass attempt.

"Just seeing the play and actually seeing how it happened, [I] kind of felt sorry for him because I know how much he wants to win," Bengals wide receiver Tyler Boyd said Monday. "I know how much he dedicates himself to this game."

Cincinnati had hoped Burrow was the franchise's next cornerstone quarterback when the Bengals selected the southeast Ohio product with the top overall pick in last April's draft. Almost as soon as Burrow officially arrived in Cincinnati, it was clear he was going to be the team's Week 1 starter as a rookie. The Bengals released veteran Andy Dalton, the team's second-round pick in the 2011 draft, and didn't add another veteran quarterback to the 53-man roster.

In his first 10 games, the rookie showed why he represents so much hope for a franchise that hasn't won a playoff game since January 1991. According to ESPN Stats & Information, Burrow ranks fourth in NFL history for the most passing yards in a player's first 10 games (2,688 yards, including his total from Sunday's game). At the halfway mark of the season, Burrow was on pace to break Andrew Luck's record for most passing yards by a rookie (4,374).

Veteran quarterback Brandon Allen, who was added to the practice squad in September as the team's emergency quarterback, was promoted to the 53-man roster along with offensive lineman Quinton Spain.

Allen and Ryan Finley, who was the team's primary backup QB and started three games last season, are among the options to replace Burrow. Taylor hinted at the possibility of the team signing an additional quarterback to replace Allen as the emergency quarterback.

Taylor said the fact Burrow entered the NFL without a normal offseason because of the pandemic restrictions is a good sign for the former top overall pick in 2021.

"He's an expert in missing an offseason and playing effectively," Taylor said. "So, I do have that to fall back on and I know that about Joe. There won't be any guesswork in how he handles it. We've seen that firsthand. That part is encouraging."