The Tigers said Tuesday that the 33-year-old Martinez tore his left ACL last week during offseason conditioning. An MRI exam Monday in Lakeland, Fla., revealed the injury.
The team said the slugging designated hitter will be re-examined next week and surgery is expected.
Martinez hit .330 with 103 RBIs in 2011, helping Detroit win the AL Central in his first season with the Tigers. He signed a $50 million, four-year contract before last season.
Martinez and Miguel Cabrera were a formidable pair in the middle of the lineup, and manager Jim Leyland had nothing but nice things to say throughout the year about Martinez's upbeat presence in the clubhouse.
Although he spent some time on the disabled list early in the season with a right groin problem, Martinez was still able to play 145 games. He was brought in to fill the DH spot and also play occasionally behind the plate, but by the end of the season, it was hard for him to catch. Detroit signed Gerald Laird this offseason to be its backup catcher.
Martinez also hurt his ribcage during the postseason.
It's been a quiet offseason so far for the Tigers, who added reliever Octavio Dotel but kept their everyday lineup largely intact. With Martinez out, they might need to make another move to replace his bat. The pressure will also fall on Cabrera, catcher Alex Avila and shortstop Jhonny Peralta to repeat the productive seasons they had at the plate in 2011.
Detroit won its division by 15 games last year and reached the AL championship series, but if the Tigers were favorites in the AL Central heading into this season, their outlook just became a whole lot murkier.