NFL.com's Ian Rapoport reported via Twitter on Wednesday that Garrard told two Jets players he no longer planned to be with the team.
According to NFL.com's Adam Schein, Garrard sent him a text message Wednesday that said "Having to call it quits. My knee is not holding up. Continuing to swell after practices. Limiting what I can do."
Associated Press reported later that a person familiar with the decision said Garrard plans to retire because of lingering knee issues.
A knee injury sidelined Garrard all of last season, and he hasn't played in an NFL game since 2010. He was the Jacksonville Jaguars' starting quarterback from 2007 to 2010 and had one great season, in 2007, when he led the Jaguars to an 11-5 record while passing for 18 touchdowns with only three interceptions.
Garrard's leaving enhances the chances of Mark Sanchez to remain the Jets' starting quarterback.