The comedian was seen without shoes on after taking the classes in an attempt to get fit.
Brand told WENN: "What happened was this foot here has become hurt from what I can only describe as kicky boxing.
"I call it kicky boxing. Kickboxing sounds so aggressive. I've been doing, like, kickboxing."
The star played down his injury, adding: "It's not like I kicked someone so hard, a bit of my foot fell off." He also referred to it as a 'rug' burn' rather than a serious problem.
Brand has chosen not to wear shoes for a while due to his current injury. He commented on general footwear: "I mean, shoes are, in themselves, an oddity and addition."