Johan Santana nearly saved the Mets’ season on one leg.

Just four days after his complete-game gem against the Marlins, the Amazin’s ace had arthroscopic surgery yesterday to repair torn meniscus in his left knee.

The Mets described the previously unannounced procedure as minor and said they expect the two-time Cy Young winner to make a complete recovery for the start of spring training. A source close to Santana said the injury resulted from “normal wear and tear” over the course of the entire season and not from any specific moment or play.

The source said the injury got more painful as the year progressed, but Santana chose to pitch through the pain and wait until after the season to have it repaired.

“He had [the injury] all year,” the source said.

In a statement, Mets general manager Omar Minaya said the injury was discovered during a standard exit physical Monday. The only time Santana had complained about the pain was after his start Sept. 18 at Washington.

The fact Santana was hobbled by knee pain made his clutch performance the final week of the season even more incredible.

With the Mets scrambling to make the playoffs, Santana threw a three-hit complete game shutout of the Marlins last Saturday on short rest. Santana threw 117 pitches against Florida that day after throwing a career-high 125 pitches in a 6-2 win over the Cubs four days earlier. Santana’s victory over the Marlins staved off elimination for the Mets for one day. Their 4-2 loss to Florida on Sunday in a do-or-die situation gave the Brewers the NL’s wild card.

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The Mets scheduled a telephone news conference for today to announce a new contract for Minaya. It’s believed to be a four-year deal.

After Minaya’s deal is finalized, the Mets likely will turn their attention to a contract for Manuel.

bhubbuch@nypost.com