The former Welsh international was rushed to a doctor yesterday (January 31) after he woke up with a swollen foot.
According to The Sun, Thomas initially went to Thursday morning's rehearsals before coaches ordered him to have the problem looked at by medics.
The rugby player was later prescribed a course of strong antibiotics, and told to rest until doctors have deemed him fit to return to the ice.
"Gareth woke up [Thursday] morning and his foot was terribly swollen," a source told the paper. "He went to rehearsals but the coaches ordered him straight off the ice. He was taken to a doctor, who diagnosed him with an infection - caused by spending so much time in skates - and prescribed him antibiotics.
"He didn't rehearse today and has been told to come back to the rink tomorrow, when medics will decide whether or not he is fit to skate," the insider continued.
"We are hoping it will not stop him from appearing on the show at the weekend, but it all depends on how well the infection heals over the next few days.
"If he does manage to make it onto the ice it will certainly be very painful for him, so it will almost certainly impact on his performance."
[Gareth Thomas jokingly posts a picture of 'slipper skates' to Twitter]
Thomas took to Twitter this morning (Friday, February 1) to joke about the situation.
"Hoping I can get my foot in my boot this morning. No pain no gain!!!!!;(" he told his followers.
A couple of hours later, he posted a picture of a pair of slippers with skating blades with the caption: "Think I may have to wear these Sunday ;)"
It was reported last month that Thomas is considering purchasing a £300,000 ice rink in order to continue with the sport after the competition finishes.
Dancing on Ice continues on Sunday (February 3) on ITV.
Dancing on Ice accidents and malfunctions - photo gallery: