Indianapolis Colts quarterback Andrew Luck could be out for up to six weeks after sustaining a lacerated kidney and torn abdominal muscle in the fourth quarter of Sunday's win over Denver.
Coach Chuck Pagano said Luck was sore after the game and felt worse late Monday before being sent for tests which revealed the full extent of the problem.
The injuries will not require surgery and a full recovery is expected. The news means that 40-year-old Matt Hasselbeck will be back in the starting role for the foreseeable future.
Pagano said: "It's way too early to guess how long Andrew will be out. We're going to keep listening to the doctors and evaluating his progress on a week by week basis.
"We've got all the confidence in the world in Matt Hasselbeck and we're not going to put Andrew back out there until he's healed and ready to go."
Hasselbeck helped the team win two games when deputising for Luck earlier in the season when the latter had a shoulder injury.
The Colts, who have a 4-5 record this season, have a one-game lead over Houston in the AFC South.