Walker was cut Monday during training at San Jose's American Kickboxing Academy.
The injury required multiple stitches, forcing the former running back to pull out of his scheduled Strikeforce fight against Scott Carson in St. Louis on Dec. 4.
"I feel terrible about this," Walker said. "I know things like this happen in all sports, but I had trained very hard and was excited to be returning to the cage again. I hope to fight again as soon as the cut heals."
The 48-year-old Walker has been pursuing MMA as the latest endeavor in his eclectic athletic career since 2007. The 12-year NFL veteran and former Georgia star also ran track, earned a black belt in taekwondo and trained for the U.S. Olympic bobsled team.
Walker made his pro MMA debut last Jan. 30, stopping Greg Nagy in the third round. He has been training in San Jose for several months.