"Right before she was supposed to have the baby, I tore my pectoral muscle completely off my skeleton," Hammer, 30, explained to host Jimmy Kimmel. "I was in the gym with my brother-in-law, John, we were just working out. Basically, what happened is I tore my pectoral muscle. They went in and they opened it up and they go, 'Your muscle is frayed. You don't live very gently, do you?' I was like, 'No, I've never been accused of that.'"
He continued, "So, I'm walking around my house -- really kind of hobbling -- and my arm doesn't work. It's really kind of a sad thing. And my wife finally goes, 'You know what? Just go get the surgery. Honestly, you're not doing anybody any favors.'"
At the time he went for surgery his wife Elizabeth Chambers, 34, chief correspondent of the Human Rights Foundation, was already overdue.
Kimmel shared a picture of Hammer in a hospital bed while kissing his wife's baby bump. His wife had posted the photo on Instagram with the caption, "Dear baby, Please don't come in the next 5 hours. Thank you, Mom and Dad."
"Usually the mother will go into the bed and the father will stand beside her," the late-night host quipped.
"We like to mix things up and keep it interesting," Hammer joked.
Things got even more interesting after Hammer's surgery.
"Really, what happened was I go in for the surgery and then I wake up in another hospital, and all of a sudden my wife is having the baby," he said. "You know, 'cause I'm on medication and all that."
Kimmel quipped, "What an impression you made on the kid!"
"I know. He slapped me!" Hammer joked. "'Wake up!'"
Hammer and his wife were married in 2010 and welcomed their second child on Jan. 15. They are also parents to 1-year-old daughter Harper.