MINNEAPOLIS -- Catcher Jesus Montero, who was demoted to Triple-A Tacoma on May 23, was diagnosed with a torn meniscus in his left knee on Saturday and will undergo surgery next week, the Mariners announced.
Montero, 23, is expected to miss 4-6 weeks.
The highly-regarded youngster was sent down after hitting just .208 with three homers and nine RBIs in 29 games for Seattle. He batted .260 with 15 homers and 62 RBIs in 135 games in 2012 for the Mariners after being acquired from the Yankees in a trade for Michael Pineda.
Montero hit .250 with three doubles and a triple in seven games with Tacoma, but didn't play the past two days. He'd been playing mostly first base with the Rainiers, as the Mariners are attempting to transition him to the new position.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.