Harrison threw 60 pitches on Friday for Triple-A Round Rock but had to be removed from the game three pitches into the fourth inning after experiencing numbness in his left hand.
Harrison, the Rangers' Opening Day starter this season, made two starts before being placed on the disabled list on April 11.
The left-hander visited with team doctors Dr. Keith Meister and spine specialist Dr. Drew Dossett on Monday, and the Rangers and Harrison were advised to shut things down for the rest of the season. Harrison was diagnosed with left elbow inflammation, which may have been caused by overcompensating because of the back, doctors said.
Harrison had a follow-up on Tuesday with Dr. Dossett, who performed two surgeries on the pitcher in April and May. There is nothing structurally wrong with Harrison's back, and the Rangers also aren't concerned about the elbow.
"There's nothing that we're concerned about at this point," Rangers general manager Jon Daniels said. "It was a significant injury, real surgery and we have every expectation he'll be 100 percent by this offseason and certainly by spring training. We were hoping to have him back this season, but it's not going to happen."
Harrison had passed all of the tests leading up to his rehab starts. He made three starts in all.
"We don't want a guy doing real damage compensating for the back with his arm," Daniels said.
Harrison had a pair of surgeries in late April and early May for an inflamed nerve in his back.
An 18-game winner last season, Harrison signed a $55 million, five-year contract during the offseason. He was affected by the injury this season, going 0-2 with an 8.44 ERA as he tried to pitch through the soreness.