INDIANAPOLIS -- Colts quarterback Anthony Richardson is undergoing an MRI on his injured shoulder but the initial belief is it's a sprained AC joint, a source told ESPN's Adam Schefter.
Richardson was injured in Sunday's 23-16 win over the Tennessee Titans after getting tackled on a 4-yard run with 4:39 left in the second quarter.
Richardson's right shoulder took the brunt of the impact as he fell to the turf, and he immediately reacted by pointing to his shoulder as he lay on the ground.
He was helped up after being attended to by the team's training staff for a few minutes and was briefly examined in the sideline medical tent before being escorted to the locker room, unable to move his right arm.
Colts tight end Mo Alie-Cox was also ruled out in the second half due to a concussion.
This is just the latest injury concern for the No. 4 overall pick in April's draft. Richardson took a hit to his right knee in the season opener against the Jacksonville Jaguars and was pulled from the game by coach Shane Steichen for the final few plays as a result.
The following week, against the Houston Texans, Richardson sustained a concussion in the second quarter and missed the rest of that game and the following week against the Baltimore Ravens.
Including Sunday's game, Richardson will have played in just 12 of a possible 20 quarters played by the Colts this season.
Gardner Minshew came in to relieve Richardson. Minshew has 25 career starts and was the Colts' starter in their victory over the Ravens in Week 3.
The Colts have been aggressive in their usage of Richardson as a runner as his dual-threat style has presented real challenges for defenses. They ranked fourth in the NFL entering Week 5 in quarterback designed runs.
But given Richardson's injuries, the Colts will face questions about how that approach exposes him to additional hits.
"I think when you have a dynamic player like him, obviously, one of his skillsets is a runner [and] that makes him really good," coach Shane Steichen said. "The designed run that he got hurt on [was] something similar to last week where he popped it for a big one.
"So that's stuff that you've got to look at, be smart with."