Indianapolis Colts quarterback Andrew Luck has been placed in concussion protocol, according to ESPN’s Adam Schefter. Shortly thereafter, NFL Network’s Ian Rapoport has reported that Scott Tolzien will be starting in place of Luck.

After Sunday’s game against the Titans, Luck had shown concussion-like symptoms, forcing the protocol. This is bad news for the Colts, who play the Pittsburgh Steelers on Thanksgiving, giving Luck less time than usual to recover, and putting his status for the game in question.

Many people have pointed to this play being the one that concussed Luck:

I believe this is the play that led to Luck's concussion. Watch his head hit the turf. pic.twitter.com/h1bW4n8DlV — Zak Keefer (@zkeefer) November 21, 2016

The process for Luck to complete the protocol in a matter of a few days isn’t ideal, and put the Colts in an extremely tough spot, who are already in the thick of a divisional race with the Texans and the Titans, who they beat on Sunday.

There are a bunch of observable symptoms that are looked for in the concussion protocol, as well as a five-step process which players must complete to return from a concussion.

Tolzien is in his sixth NFL season. He came into the league in 2011 out of Wisconsin as an undrafted free agent, and signed with the Chargers, where he only made preseason appearances. He was then claimed by the 49ers off waivers, and was a backup, until being released in August of 2013.

He was then signed by the Green Bay Packers, and was released last season. He signed with the Colts in March of 2016.

Tolzien has started just two games in his career, both coming in 2013 with the Green Bay Packers. He is 0-1-1 in those two starts, and on his career, has a 61.5 completion percentage, 721 yards, one touchdown, and five interceptions thrown.

Luck was not at practice on Monday, which raised concerns, and now we understand his absence.

On the season, Luck has completed just under 63 percent of his passes, for 2,827 yards, with 19 touchdowns against eight interceptions.