The Rangers had sent Harrison, who has been out since early April, on a minor league rehab assignment in hopes of him returning to the team. He had most recently started for Triple-A Round Rock on Friday and threw 60 pitches, but left the game with numbness in his left hand.
Harrison was originally placed on the disabled list on April 10 with what had been diagnosed as a lower back strain. After a pair of epidural injections, it was determined that the left-hander would have to undergo back surgery for a herniated disc. A setback later in the month would force him to have a second procedure done.
The team had hoped for Harrison to return in September to help with a postseason push. He had been throwing off a mound since shortly after the All-Star break, and had been on a rehab assignment since late July. After Harrison experienced numbness, the team chose to not risk causing long-term damage to the 27-year-old and will instead get him some rest in hopes he returns at full health for Spring Training next year.
Harrison had made two starts for the Rangers in April before going down with the injury. He allowed 10 earned runs over 10 2/3 innings pitched.