It turns out that Charles bruised his foot while carrying a box from Scanlon Hall, the players' dorm at Missouri Western State University, to a nearby parking lot last week when the Chiefs broke training camp.
Charles did not accompany the Chiefs to Charlotte, North Carolina, for Sunday night's 28-16 preseason loss to the Carolina Panthers.
"He came down a grassy slope there and just kind of rolled his foot over on the curb," coach Andy Reid said. "It was that simple. That was it. He went up to [trainer Rick Burkholder]. ... He was hurting that night, and the next day he woke up and he was feeling a little bit better, and he's feeling better today.
"We're optimistic about it. Initially there was some concern. He had all the stuff done on it, the X-rays, the MRIs and all that done on it. Everything is clear."
Kansas City was off from practice Monday. Reid said he was unsure whether Charles would be able to participate when the Chiefs get back to work Tuesday.
The Chiefs continue their preseason Saturday night against the Minnesota Vikings at Arrowhead Stadium.