The Wedding Crashers star hit the waves near his home in Hawaii, and ended up in a nearby hospital after slashing open his forehead.
He explains, "This was a few weeks ago. I took on a wave that was probably too big for me. I went off the back and the board kinda caught me and came back and hit me in the forehead and I got 24 stitches."
Wilson was dripping blood as he paddled back to the shore and admits he was a little fearful of an encounter with a shark - because his accident happened in the same place where his older brother Andrew was "attacked" last year (10).
He says, "Believe me, I was thinking about the (shark) as I was paddling back in with a little blood dripping in to the same cove where my brother was attacked recently! And I had to go to the same doctor who stitched Andrew up, so this guy just thinks we're lunatics."
Wilson reveals Andrew has since recovered from the shark bite and is now boasting about surviving the incident.
The actor adds, "My brother... was out of the water for a while, and he went through this whole progression of being kinda scared and not going back in the water, to going back, and then kinda proud.
"He's like, 'Not many people can say they got a business card from the man in the grey suit and live to talk about it!' That's what he's calling the shark now! So now he's kinda proud of it. First he was bit, now he (says he) was attacked!"