NEW ORLEANS – New Orleans Saints quarterback Derek Carr suffered an oblique injury during Monday night’s loss to the Kansas City Chiefs, a source confirmed to ESPN.

An MRI performed Tuesday confirmed that the injury was to Carr’s oblique, according to the source. The quarterback had said he believed he suffered the injury when he threw an incomplete pass near the end of the 26-13 loss, but had to undergo additional testing to confirm it.

The source would not put a timeline on how long Carr will be sidelined.

Oblique injuries usually lead to absences of several weeks. The Saints play two games in ten days: Sunday against the Tampa Bay Buccaneers and then on October 17 against the Denver Broncos on “Thursday Night Football.”

If Carr can’t play, rookie Spencer Rattler or Jake Haener would take his place. Haener replaced Carr against the Chiefs.

The obliques, or abdominal muscles, can affect a quarterback because most of his throwing power comes from his core muscle rather than his arm. Carr said he didn’t leave the Chiefs game because of pain, but because he wouldn’t be effective if he returned.

“It wasn’t like dealing with pain. … I just can’t do what I want to do,” he said at the time.

Former Saints quarterback Drew Brees returned from a left oblique strain after missing two weeks of training camp prior to the 2014 season. Brees, who was 35 at the time of the injury, later admitted that his mechanics suffered and that he developed bad habits that season after rushing to get back into the lineup before he was fully healthy.

Carr has suffered four serious injuries in New Orleans, though he missed no time last year. He sprained the AC joint in his shoulder against the Green Bay Packers in Week 3 of last season and was placed on concussion orders twice last year in losses to the Minnesota Vikings and Detroit Lions.

Carr suffered a left groin injury in Week 4 this season.

NFL Network first reported the news that those additional tests confirmed Carr’s injury was to his oblique.