ESPN Packers reporter Rob Demovsky explains how a PGA Tour event could reveal how Aaron Rodgers is recovering from knee surgery. (1:21)

GREEN BAY, Wis. -- Packers quarterback Aaron Rodgers had a legitimate reason for pulling out of the Pro Bowl.

Rodgers underwent knee surgery within days of the team's Jan. 17 playoff loss to the Arizona Cardinals, he confirmed to ESPN on Friday night.

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One source described the surgery as a minor scope and a "cleanup of an old injury."

Rodgers told ESPN that he is "doing well" and "recovering on schedule."

It's unclear when Rodgers' knee became an issue this past season, but he was hit on his left knee by Detroit Lions defensive end Ezekiel Ansah on Nov. 15. After the game, Rodgers described the hit as "a little low" and said he was sore. The following week, the Packers listed Rodgers on the injury report, but for his shoulder, not the knee.

It was the only week that Rodgers was listed with an injury. He played in all but 10 of the Packers' offensive snaps this past season and did not miss any practice time because of the knee.

The injury could help explain, at least in part, why Rodgers' production dropped in 2015. He set career lows for completion percentage (60.7), passing yards per game (238.8) and yards per attempt (6.7).

Rodgers had reconstructive surgery on his left knee in January 2004, after his first season at the University of California. Doctors repaired a torn ACL that Rodgers said he suffered years earlier while playing basketball in high school. He returned for the start of his second and final season at Cal.

Barring a setback in his recovery, Rodgers is likely to be ready to participate when the Packers begin their offseason program in April.