The Knicks said Smith's injuries, which were treated at the Hospital for Special Surgery in New York City by team orthopedist Dr. Answorth Allen, were chronic and gradually worsened. His recovery time is approximately three to four months, which could make him available between Oct. 15 and Nov. 15 -- near the start of the 2013-14 season.
A league source told ESPNNewYork.com that the Knicks were aware Smith likely would need surgery for his left knee, which started bothering him during the playoffs. At the time, he had fluid in his left knee, according to a source.
Last week, he re-signed with the Knicks for three years and approximately $18 million, Smith's agent, Leon Rose, confirmed to ESPNNewYork.com. The New York Times earlier reported the new parameters of the deal. It was widely reported in early July, including by ESPN.com, that Smith's deal was for $24.7 million over four years.
Rose said Smith and the Knicks originally agreed to a four-year contract but Smith opted to shorted it to three-year deal so he has the option to test free agency.
"Re-signing J.R. was one of our primary goals this offseason, and we are thrilled to have him back," Knicks general manager Glen Grunwald said in a statement. "He made great strides this past season with his consistent play off the bench for us, and we look forward to his continued growth."
Smith, 27, became just the third player in franchise history to win the Sixth Man Award, joining John Starks and Anthony Mason. Smith averaged career highs in points (18.1), rebounds (5.3) and minutes (33.5) in 80 games off the bench last season.
This past October, Smith's younger brother, Chris, who's currently playing on the Knicks' summer league team in Las Vegas, underwent left patella tendon surgery.
Jared Zwerling is a regular contributor to ESPNNewYork.com. Information from ESPNNewYork.com's Ian Begley contributed to this report.