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The New York Mets have placed LHP Johan Santana on the 15-day disabled list with lower back inflammation, and according to GM Sandy Alderson, he is not expected to pitch again in 2012.

An MRI taken on Santana’s ailing back Tuesday revealed the inflammation but uncovered no major structural damage. Doctors have prescribed rest, medication, and intermittent exercise as a course of rehabilitation, and it is believed that the lefty won’t need surgery.

“I can’t say that this is a shock or a surprise,” Alderson told reporters in a news conference at Citi Field on Wednesday. “It’s disappointing, but that’s the nature of it.”

Santana is 6-9 with a 4.85 ERA in 21 starts this season, and has struck out 11 batters (against just 39 walks) in 117 innings. He also pitched the first no-hitter in Mets history on June 1, a 134-pitch outing against St. Louis that ended 50 years of team no-hit drought, but his season has suffered a bit since; Santana was 3-2 with a 2.38 ERA after that victory, but is just 3-7 with a 7.47 ERA in 10 starts since and also spent three weeks on the disabled list with a sprained ankle.

All that said, this season has to be considered a success for Santana, who missed the very end of 2010 and all of 2011 after major shoulder surgery. Manager Terry Collins said in Spring Training the Mets hoped to get 28 starts out of Santana, and Alderson said Wednesday that the lefty had “accomplished quite a lot” this season and “should be ready to go” in 2013.

The Mets will recall Collin McHugh from Triple-A Buffalo to take Santana’s spot in the rotation, and the 25-year-old righty will make his Major League debut in Thursday afternoon’s series finale with Colorado. McHugh, who was the Mets’ 18th-round pick in the 2008 MLB Draft, was 2-4 with a 3.39 ERA in 12 starts for the Bisons this year.

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