Pence said he was in a hot tub and got out to use the bathroom. He had left the door open, but didn't noticed that a friend had just closed it. He hit it with his shoulder, leg and head and it shattered.
The 24-year-old outfielder said the injuries weren't as bad as they looked.
Pence hit .322 with 69 RBIs and 30 doubles as a rookie in 2007. He finished third in NL Rookie of the Year voting, behind Ryan Braun and Troy Tulowitzki.
The Astros held their first full-squad workout Tuesday, but Pence couldn't even straighten his finger or his left leg.
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