Steven Thompson was left "mortified" after a joke in training left St Mirren team-mate John McGinn with a cut in his thigh.
During a drill last week, Thompson was robbed of the ball by McGinn, and then threw a spiked pole at the Scotland Under-21 international in jest.
Unfortunately, the pole speared McGinn in the leg, causing him to miss St Mirren's 4-1 win over Kilmarnock on Saturday.
"I've been shocked by it, to be honest, really down about it," Thompson told the Scottish Sun.
"I like a laugh and a joke in training, but for something like this to happen is just unbelievable.
"The pole went about a centimetre into his leg and he's obviously got quite a bad injury. The word seems to be he'll be out for around three weeks.
"I think he's torn his muscle slightly and, while he needs to make sure it heals properly, there isn't going to be any long-term damage.
"I'm just mortified by the whole thing. It was a daft prank. It wasn't like I threw the pole out of anger or anything like that. That's not what happened.
"I threw it for a laugh, stupid me trying to be funny, and unfortunately it's anything but. It's a total disaster."
