The Colts became the first team to beat the Broncos this season with a 27-24 victory at Lucas Oil Stadium, but the win came at a cost as Luck sustained a lacerated kidney and partial abdominal tear.
Neither injury will require surgery but, while head coach Chuck Pagano refused to put a timeframe on Luck's return, the 26-year-old is expected to be sidelined for between two and six weeks.
"The injuries happened at the end of an early fourth-quarter scramble when Andrew was doing everything he could to get us the win," read a statement from Pagano.
"Andrew was sore after the game and was feeling a little worse Monday afternoon so we sent him to get tests. 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."
The Colts are currently 4-5 for the 2015 season and are not back in action until November 22, when they take on the Atlanta Falcons.