O'Neill believes that modern boots are "flimsy" and admits that he doesn't know how his players perform in them.
The Northern Irishman said: "It makes me laugh, the players of today. There was an incident in training yesterday when someone stamped on Steven Fletcher's foot. You know he is limping round for two or three minutes and you're kind of glad.
"The boots are so flimsy. If anyone stands on them, you are going to get injured, like a punctured toe, because there is nothing to them.
"These injuries are to do with the boots which are so light. Now, the boots they wear, the studs — or the lack of studs — I honestly don't know how they stand up in them. I genuinely do not know how they do it."
Sunderland are currently 13th in the Premier League.