The 42-year-old actor, who welcomed baby Robert last month, said that he was afraid that the blood pouring from his injury would attract the man-eater.
Appearing on The Tonight Show with Jay Leno, he explained, 'I took on a wave that was probably too big for me.
'I went off the back and the board kinda caught in the air and came back and hit me in the forehead and I got 24 stitches.
'I was thinking about the shark as I was paddling back in - with a little blood dripping - into the same cove where my brother was attacked recently.'