According to ESPN NFL Insider Adam Schefter, Andrew Luck has informed the Colts he is retiring from the NFL:
Filed to ESPN: Andrew Luck has informed the Colts he is retiring from the NFL, per source. There will be a press conference Sunday to make it official, but Luck is mentally worn down, and now checking out.
— Adam Schefter (@AdamSchefter) August 25, 2019
Luck has battled serious injury issues his entire NFL career, missing an entire year two seasons ago, and has been struggling with ankle and hamstring injuries this preseason.