He later tweeted an update on what exactly happened.
"Hey, guys. I didn't injure myself doing a stunt or anywhere near the set of 'Shooter,'" he wrote on Monday. "I was the victim of a freak accident during a family outing on Sunday. My leg is badly broken & required surgical attention, but I will make a full recovery, am in good hands."
Phillippe added he plans to be "back in action soon" and thanked everyone for their concern.
"Thank you for all the well wishes, support, & concern. also a special thanks to the paramedics & first responders who helped me at the scene & to the medical staff caring for me now. I will keep you updated on my progress"
The actor is currently starring in Shooter on USA, which premieres on Tuesday at 10 p.m. ET.
WATCH: EXCLUSIVE: Ryan Phillippe on Embarrassing His Kids & Daughter Ava Looking Like Reese: 'She Has Her Own Face!'
Phillippe recently opened up to ET about embarrassing his kids, Ava and Deacon. To see what he said, watch the exclusive interview, below!