St Johnstone midfielder David Robertson broke his leg during Wednesday's loss to Hibernian, manager Steve Lomas has confirmed.
The 26-year-old left the field on a stretcher after coming on as a second-half substitute at McDiarmid Park and was taken to Perth Royal Infirmary, where he spent the night.
Lomas told the club's website: "I've been up to see him this morning and he had already seen the specialist who unfortunately has confirmed that it is a break. He'll be operated on this afternoon.
"I'm gutted for him. Robbo's a great guy to have around the place and I felt he was showing signs in recent weeks of being able to make a bigger contribution to the team.
"We wish him well and I know the lads will rally round him."
Robertson confirmed the leg break on Twitter, saying: "Thanks everyone for the messages of good luck, it's really appreciated but unfortunately not good news. Broken leg as expected, getting an op today!"