Tennis superstar Andy Murray says he's in some serious pain after undergoing hip surgery in London early Monday morning -- but even worse ... the guy thinks he's fat.
The 31-year-old Wimbledon champ has been in so much pain from his messed up hip over the past 2 years that he's considered retiring from tennis if the doctors can't fix him up.
So, he went under the knife on Monday -- and seems to be optimistic.
"I underwent a hip resurfacing surgery in London yesterday morning...feeling a bit battered and bruised just now but hopefully that will be the end of my hip pain," Murray said.