General manager Chris Ballard broke down the recent problems with the injury, via Stephen Holder of The Athletic:
Stephen Holder @HolderStephen
Ballard says it's a calf injury... wasn't getting better.... in course of dealing w it he developed ankle issue... They explored an area near the bone and it does not appear to be the issue... focus has shifted elsewhere.... Saw another expert and there's a high ankle-like issue
The 29-year-old has been dealing with the calf injury since April, causing him to miss Indianapolis' OTAs and portions of the team's training camp.
"At times, I do worry about it," Luck told NBC Sports' Peter King on Aug. 6, referring to his calf. "It can be frustrating. The arc of an injury, whether it's a big surgical one or something you're rehabbing through."
It turns out he's still dealing with the issue, adding to what's already a troubling injury history.
The four-time Pro Bowler missed all of 2017 due to a persistent shoulder injury dating back to the 2015 season that required surgery in Jan. 2017. Luck also missed significant time in 2015 with a lacerated kidney and partial abdominal tear.
Last season, Luck appeared in every game for the Colts and was named the 2018 NFL Comeback Player of the Year. Through the regular season, he tossed for 4,593 yards and 39 touchdowns—one fewer than his career-high 40 touchdowns in 2014—on 67.3 percent completion. Indianapolis earned a 10-6 record after going 4-12 without him in 2017.
Considering how proficiently Luck bounced back in 2018, this calf injury has to be discouraging for the Colts.
If Luck is kept off the field, head coach Frank Reich can lean on backup Jacoby Brissett. The 26-year-old started 15 of 16 games during Luck's 2017 absence, passing for 3,098 yards, 13 touchdowns and seven interceptions. Since entering the league in 2016, Brissett has a 59.1 completion percentage.
The Colts open the regular season against the Los Angeles Chargers on Sept. 8.