Indianapolis Colts left tackle Anthony Castonzo is out for the rest of the season and will undergo ankle surgery.

Head coach Frank Reich said Wednesday that Castonzo won’t play Sunday in the regular-season finale. Beating the Jacksonville Jaguars puts the Colts in position to make the playoffs, but they’ll need help to avoid missing out on the postseason with an 11-5 record.

Reich said the Colts are considering moving Pro Bowl guard Quenton Nelson to left tackle.

When the Colts first lost Castonzo and Le’Raven Clark in back-to-back games, Reich used Nelson at left tackle.

“Quenton is Quenton Nelson,” Reich said earlier this month. “And that spot is very important, so we knew that if we put him out there, he’s the kind of player that would rise to the occasion.”

Castonzo’s loss is a major blow to the Colts’ offense. Reich said he was unfamiliar with the specific surgical procedure recommended for Castonzo but doesn’t believe the injury is career-threatening.

A first-round draft pick by the Colts in 2011, Castonzo has been an anchor of the offensive line, playing in 144 games (all starts) over 10 seasons.

Offensive tackle issues have thinned the Colts’ line. Clark (Achilles) is out for the season, Braden Smith is coming back from the reserve/COVID list and Will Holden is unavailable this week.

Unless Nelson moves to left tackle, Castonzo’s surgery could leave the Colts with J’Marcus Webb and Chaz Green as the primary offensive tackles.