The move could raise questions about Kitna's future in Detroit.

There had been speculation the Lions (0-5) might trade Kitna and rely instead on backups Dan Orlovsky and Drew Stanton. But a trade didn't materialize. Instead, the Lions sent wide receiver Roy Williams to Dallas for draft picks.

Kitna suffered a back injury in a loss to Chicago two weeks ago. He did not play last week against Minnesota.

Orlovsky played in Kitna's place against the Vikings. He likely will make his second career start at Houston on Sunday.

Kitna declined comment Tuesday, but had told The Associated Press on Monday he expected to play again this season and that his injury wasn't that serious. Also on Monday, Coach Rod Marinelli wouldn't answer questions about Kitna's health.

"After extensive examination and consultation with the team medical staff, it became clear that placing Jon on injured reserve was the right decision," Lions general manager Martin Mayhew said in a statement. "Jon and I met today and discussed moving forward with respect to his rehabilitation which will be done in coordination with our medical staff."

The Lions said Kitna's injury represents "an acute exacerbation of a chronic condition."

Kitna had 758 yards passing this season with five touchdown passes and five interceptions before back spasms sidelined him against Chicago on Oct. 5.

Kitna had started 36 straight games until Orlovsky played in Sunday's 12-10 loss at Minnesota.

Orlovsky was 12-of-21 for 150 yards and a score. The fifth-round pick from Connecticut in 2005 also rolled out of the end zone for a safety.

Stanton has not played in the regular season as a pro.

Kitna had an MRI last week and was evaluated by a specialist, but had declined comment on his health.

Kitna had 4,000-plus yards passing in each of the past two seasons in Detroit and combined to throw 39 TDs and 42 interceptions.

He has thrown 152 TDs and 151 interceptions in 115 games for the Seattle Seahawks, Cincinnati Bengals and the Lions since making it to the NFL as an undrafted free agent in 1997.