ST. LOUIS (AP) — The NFL is investigating whether correct concussion protocol was followed for Rams quarterback Case Keenum late in Sunday's loss at Baltimore.

St. Louis coach Jeff Fisher said Monday the system failed because of a "combination of unusual events" and believed that nobody in particular was to blame.

A league spokesman said a review was begun after the game "to determine the facts of the injury ... and why (Keenum) was not removed from the game for the necessary evaluation by a team physician or the unaffiliated neuro-trauma consultant, as required by our concussion protocols."

That review is continuing through discussions with the Rams and their medical staff, the ATC spotter, game officials, NFL medical advisers, and the players' union.

"The appropriate thing is to get everybody together and just make sure it doesn't happen again," Fisher said. "We've got to get it straightened out."

Fisher believes the independent sideline observer decided not to get involved because Rams trainer Reggie Scott came on the field to examine Keenum with 1:04 remaining and the game tied at 13.

"Because he saw our head trainer on the field, he didn't feel it was necessary to make the call," Fisher said. "And for whatever reason, we went on with the two plays."

Fisher inferred that Scott had to make a snap judgment before being told to return to the sideline, also noting that play clock had been started.

"He spoke to Case and he questioned Case, and Case said he felt OK," Fisher said. "Reggie made the right decision to go out there."

If Scott had questioned Case further on the field, Fisher had been concerned the Rams might have gotten charged with their final timeout.

Fisher said he didn't see Keenum's helmet hit the turf on a hit by Tim Jurnigan. He said he'd been in "game management mode."

"I saw Case go down, but I didn't see anything else that took place," Fisher said. "I didn't see him struggle to get up."

Fisher didn't learn Keenum had sustained a concussion until after his post-game news conference. The coach is hopeful Keenum will clear the concussion protocols and be able to start this week at Cincinnati.

"Fortunately, Case feels really good," Fisher said. "He feels much better today."

The NFL plans to reinforce the procedures for this week, with three games scheduled for Thanksgiving Day.

After the hit, Keenum's hands immediately went toward his head. He struggled to get up, appearing staggered and backup Nick Foles noticed, taking a few warmup throws, but he stayed in the game.

The concussion did not appear to affect Keenum's play in the final sequence. He was a little high on an incomplete pass intended for Wes Welker the play and was looking for potential receivers when poor blocking by left tackle Greg Robinson led to a sack/strip by Courtney Upshaw that set up the game-winning field goal by the Ravens' Justin Tucker in a 16-13 loss.

"Anytime you implement something, there are things you have to work through," Fisher said. "There are unintended consequences that come up."