The Lost star was in agony after a surfing accident but had no clue his injury was a broken bone until he could bear the pain no more.
And he blames the tough nature of surfing pal Kalani Robb for his efforts to walk the pain off.
Monaghan says, "Pro surfers are very tough about it (injury), so I paddled over to Kalani and said, 'I think I hurt my foot.' And he said, 'We'll catch two or three more waves and we'll go in.'
"Then we got out on the beach and he was looking for his girls, so we walked, like, 400 yards down the beach, and I'm hobbling.
"We put some ice on it and the next day (when) I woke up I couldn't even put my shoe on."