Derrick Lewis believes he has been fighting with a torn ACL for the past four years.

Lewis told ESPN on Monday that he found out two weeks before his recent loss to Junior dos Santos that he had a torn ACL in his left leg. He informed the UFC of the injury before the fight, as well. They determined, after consulting with doctors, that he was able to proceed with the fight.

Lewis said he felt his knee "go out on me" in the second round of his loss to dos Santos earlier this month. He is scheduled to undergo surgery next Tuesday.

Doctors have since informed the 34-year-old that he originally tore his ACL during his February 2015 fight against Ruan Potts when Potts went for a kneebar attempt. He also tore his MCL and meniscus in the process, too. Despite the injury, Lewis went on to win that via TKO and proceeded to go 9-4 in his next 13 fights.

He said he hopes to be sidelined for approximately six months following surgery.