Per ESPN's Chris Mortensen (via Adam Schefter), Luck may need additional surgery after doctors expressed concern over his right shoulder.
Colts owner Jim Irsay announced in January 2017 that Luck had outpatient surgery to fix an issue that dated back to 2015. The 28-year-old wound up missing all of last season as he continued to rehab his shoulder.
Mortensen reported in December it would be determined if Luck needed a follow-up procedure once he resumed a throwing program after receiving treatment in Europe.
"I believe in the process that I'm in right now," Luck told reporters in December about hoping to avoid more surgery. "I've got great help. I hope to continue to get better."
The Colts finished last season 4-12, their worst record since 2011. Luck threw for 4,240 yards with 31 touchdowns in 15 games during the 2016 season.