Cabrera, who hasn't played since Aug. 1 because of a season-ending ankle injury, had the surgery on Aug. 30.
The outfielder was experiencing back pain for three or four months, but hadn't told anyone about it, Toronto general manager Alex Anthopoulos said on Saturday before the Blue Jays' game against the Minnesota Twins. The tumor was pushing on nerves and causing weakness in his legs and causing the issues that plagued Cabrera throughout the season.
"It didn't make any sense considering he's 28 years old," Anthopoulos said. "I'm glad he finally came forward. I'm not glad that we found something, but I'm glad it can be corrected and we should be good to go."
Cabrera revealed his back pain after visiting a personal doctor and an MRI revealed the tumor.
"You give him credit because he doesn't want to come out of the lineup, wants to play, would have to be dragged to the training room, didn't want treatment, did not want to make excuses, ever, for his play," Anthopoulos said. "That's something that you admire. I think he's just relieved that now he knows he's going to be fine."
Cabrera, who signed a two-year, $16-million contract with Toronto in the offseason, will need two weeks to recover from the surgery. He finished this season with a .279 average and three home runs with 30 RBI in 88 games.
MLB's recent drug investigation began last year after Cabrera, the All-Star Game MVP for the San Francisco Giants, tested positive for elevated testosterone.