Bradford injured himself during Wednesday night's 4-3 loss against the White Sox while making his final warm-up throws on the mound with two outs in the bottom of the seventh inning. He stopped in between tosses to gather himself after feeling pain in his back and toed the rubber once more to deliver another pitch, but then signaled to Rays catcher Dioner Navarro that he could no longer throw, which brought out Rays team trainers as well as manager Joe Maddon.
Bradford said the injury did not feel any better when he woke up on Thursday morning.
"It locked up," he said. "I can't move like I need to move."
Bradford is 1-0 with a 2.08 ERA this season in 11 appearances for the Rays. The right-handed submariner spent the first 75 games this season on the disabled list while recovering from right elbow surgery and rejoined the team on June 27.
Bradford, 34, has a history with back injuries. He had surgery on his back in both 2000 and 2005 to repair herniated disks, but he said he did not feel that this particular injury was as severe.
"This is kind of one of those in between things," Bradford said. "The two times I had surgery, I knew I was going out and done. This is more like a little hiccup or bump in the road where you've got to take your time off and deal with it. Hopefully, it doesn't lead to anything worse than that."
Thayer, 28, will begin his second stint with the Rays. He appeared in three games in May, going 0-0 with a 5.06 ERA. Thayer made his Major League debut on May 22 against the Marlins and earned a save, becoming the first player in Rays history to accomplish the feat in a debut.
For Durham this season, Thayer posted a 2.01 ERA with a team-high 14 saves in 36 appearances. Thayer, a six-time Minor League all-star, was one of two Bulls players named to the International League All-Star team this season.
"He pitched well, I thought, when he came up last time," Maddon said. "I think he's going to be even more comfortable this time around. I like him. I think he's got a fine arm. He's got versatility. You can pitch him a couple innings, if necessary."
Thayer, whose Durham team was playing in Indianapolis, said he received a phone call from his Triple-A manager late Wednesday night that he would be heading to Chicago in the morning. He hopped on a quick flight from Indianapolis to Chicago and was at U.S. Cellular Field more than three hours before Thursday's game. His nameplate hadn't even been filled in yet as he sat in front of a locker assigned to him in the visiting clubhouse.
Thayer pitched in each of the last two games against Indianapolis, earning a save in one inning of work on Wednesday. Despite pitching in back-to-back contests, Thayer said he would be available to throw should the Rays call upon him during Thursday's game.
Thayer said he felt like a different pitcher from his last stint with the Rays.
"I would say I got a little better on stuff," Thayer said. "I got hit more [in Triple-A], but I thought my stuff was better down there, so we'll see where it goes. But I feel like I improved."
Jesse Temple is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.