The 36-year-old right-hander was injured while throwing a pitch during the eighth inning of Saturday night's victory over the Washington Nationals. An MRI exam Monday found a tear of the ulnar collateral ligament.
Isringhausen, who missed part of last season with the St. Louis Cardinals following elbow surgery, will undergo Tommy John surgery to repair the current damage. He was 0-1 with a 2.29 ERA in nine appearances this year.
Isringhausen's agent, Dan Horwits, told the St. Petersburg Times this was not the end of the line for the pitcher.
"This is not a retirement sendoff," Horwits said. "Knowing Jason, in every surgery he's ever had, he's come back early, so I wouldn't put it past him," Horwits said. "You never know."
Horwits said Isringhausen is scheduled for surgery Tuesday. The rehab is expected to take 10-12 months, leaving him open to return by the middle of next season.
The Rays placed Isringhausen, who has 293 career saves, on the 60-day disabled list on Sunday.
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