The left-hander was held out of his throwing session Tuesday and underwent an MRI that showed only inflammation.
"It has been a process, adding the workload and stuff," Thornton said of his early work this spring. "I'm not worried about it at all. We have time to back off a little bit. There's no reason to throw through discomfort on Feb. 19. I'm not worried about it one bit. I trust (trainer Herm Schneider) to get me ready and there will be no problem. I'll be throwing in a couple of days here."
Thornton said the discomfort is in his left arm above the elbow in the triceps area.
"It's just achy, balky, whatever you want to call it," Thornton said. "More than likely it's just the process of throwing every day for a week and adding the intensity, live (batting practice), cutting it loose a little bit. Like I said, it's something we can get under control and it won't be a problem the rest of the year."
Thornton appeared in 74 games last season matching a career-best he previously reached in 2008. He is expected to be a key member of this season's bullpen as the primary left-hander.
In 2010, Thornton spent 15 days on the disabled list with left elbow inflammation, but he said this injury doesn't remotely compare in severity to that one.
With the extra time in spring training this year as players get ready for the World Baseball Classic, Thornton is taking his setback in stride.
"It was a process where we were going to take it easy anyways and ease into things, knowing we had plenty of time to get ready," he said. "We have plenty of time not to worry about it."
White Sox manager Robin Ventura also mentioned the benefit of the longer spring training after the injury was first revealed Tuesday.
"You're concerned every time a guy has that. I'm not sure what level he's at, but again, the beauty of being down here so early is that you can give him the time off and he can catch up and there's nothing wrong with it," Ventura said.