Coach Chuck Pagano said Sunday Anthony Castnazo will be day to day after an MRI confirmed a mild MCL sprain, per Kevin Bowen of the team's official website.
The Indianapolis Colts left tackle exited in the first quarter of Saturday night's 27-6 preseason win over the Cleveland Browns with a right knee sprain. Third-year pro Joe Reitz took over for Castonzo, who was examined by trainers on the sideline.
Castonzo, the Colts' first-round draft pick in 2011, has started 27 games at left tackle for the team over the past two seasons. Colts coach Chuck Pagano said Castonzo would have an MRI on what he called "a mild MCL sprain" Saturday night.
Castonzo still struggles with aspects of his game. As the NFL's 32nd-ranked tackle last season, per Pro Football Focus, Castonzo led all offensive linemen with 36 blown blocks. He's not a premier tackle, but Indy can't afford to lose depth on its rebuilt line.
No starting passer was hit more than Luck during his rookie campaign, so Castonzo's status will be closely monitored.