Texas recalled right-hander Anthony Ranaudo from Triple A-Round Rock, the club where Gonzalez was sent. Ranaudo, a starter throughout his pro career, is expected to pitch in long relief.
Harrison will start Wednesday against Arizona, his first major league start since spinal fusion surgery in June 2014. Saturday was the deadline for Harrison to be activated from the DL after his 30-day medical rehab assignment.
Harrison never really knew what it would be like when he started his comeback from spinal fusion surgery.
Still, the Rangers left-hander never doubted that he would pitch again.
"I think success for me was getting back on the mound. ... My biggest hurdle was getting back on the mound again," Harrison said. "At this point, it's a matter of getting my mind right again to go out there and pitch in a big league game, and try to control my emotions as best as possible."
The 29-year-old Harrison's last major league start was May 13, 2014, a game at Houston he left with back stiffness.
"It's just amazing to be at this point," Harrison said.
Harrison was coming off an All-Star season in 2012 when he won 18 games, part of a two-year span when he was 32-20 with a 3.34 ERA in 63 games, when he got a new $55 million, five-year contract. Harrison had never had any back issues before then, but has since made only six major league starts.
The lefty worked through back soreness during spring training in 2013 and lost his first two starts before two epidural injections. He eventually had two operations in nine days on a herniated disk in his lower back and missed the rest of the season.
The start of his 2014 season was delayed after back stiffness during spring training. He then made four starts before being diagnosed with a condition in which a vertebra slips out of position along with significant nerve irritation before the spinal fusion surgery in his lower back.
There is no known history of a major league pitcher coming back from that type of procedure.
"I feel good physically and mechanically. Just ironing out everything is the hardest part, and learn how to pitch with less (velocity)," Harrison said. "But I'm confident in myself and command the strike zone, be aggressive and get people out."
Harrison is trying to follow teammate Colby Lewis, who had his own unprecedented comeback.
Lewis, the Rangers' most successful postseason pitcher, had surgery in July 2012 to repair a torn flexor tendon in his right elbow. His comeback from that was thwarted by the troublesome hip that had bothered him for some time before he had a resurfacing procedure in August 2013 that was just short of a full hip replacement.
After finishing strong last season, Lewis is 8-3 going into his start Sunday against the Los Angeles Angels.
"I hope I can be, I don't know if inspiration is the right word, to be a lot of different people, just with the hip. Matt can do the same thing with his back," Lewis said. "A lot of people think we've got this done and it's going to limit me in certain things that I do for the rest of my life. I think what I've done and what he's done, it opens eyes."
Texas already had a spot on its 25-man roster for Harrison after Neftali Feliz, the closer for both of the Rangers' World Series appearances, was designated for assignment after throwing two scoreless innings Friday night.
Feliz was 1-2 with a 4.58 ERA in 18 games this season, but his appearance in an 8-2 loss to the Los Angeles Angels on Friday night came after coming off the disabled list.
The Rangers have 10 days to trade, release, or outright Feliz to the minor leagues. The right-hander can decline a move to the minors and become a free agent. General manager Jon Daniels said Texas will try to trade Feliz, the former All-Star closer who developed arm issues after the Rangers put him in the starting rotation following their 2010 and 2011 AL pennants.
The 23-year-old Gonzalez (2-4), who had a 0.90 ERA through his first four major league starts, allowed six runs in 1 2/3 innings against the Angels on Friday night.
Texas has two days off next week before the All-Star break. The move with Gonzalez was made since Harrison will pitch Wednesday and Yovani Gallardo is scheduled to stay on regular rest and pitch twice before the break. Plus, the Rangers needed a long reliever after Gonzalez's short outing.
The Associated Press contributed to this report.