Mark Sanchez had arthroscopic left knee surgery this season, according to a person familiar with the quarterback’s offseason rehabilitation. The procedure was described as an “extremely minor” clean-up and occurred at about the same time that Sanchez had season-ending shoulder surgery (Oct. 8).

“It was as routine as taking Tylenol,” the source said.

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Sanchez’s 2013 campaign was cut short when he suffered a right shoulder injury in the fourth quarter against the Giants in the Jets’ third preseason game. He initially was placed on injured reserve (with the designation to return) in September, but after trying to rehab his throwing shoulder, he opted for surgery and was placed on season-ending IR.

The source said Sanchez, who was involved in a training-camp competition with rookie Geno Smith at the time of his shoulder injury, opted to get knee surgery only because he already was on IR and had the time.

Jets general manager John Idzik said Saturday at a Jets House event in Manhattan that the team is keeping close tabs on Sanchez’s recovery. The Jets, however, are expected to release him this offseason in an attempt to free themselves from his hefty contract.

Sanchez, who earned a guaranteed $8.75 million in 2013, is due a $2-million roster bonus in March and carries a $13.1-million cap hit in 2014. If the Jets trade or release him, they’ll be hit with a $4.8-million charge of “dead money,” but it would save them $8.3 million.