Kilmarnock goalkeeper Craig Samson faces weeks out of action after picking up a suspected broken toe in the 2-0 win over Dundee United.
Manager Allan Johnston told BBC Scotland: "It looks as though he broke his toe. He got quite a bad one."
The 30-year-old has been an ever-present this season since arriving from St Mirren.
But he was forced off at half-time at Rugby Park after a collision with United midfielder Stuart Armstrong.
"Obviously we're disappointed to lose him," added Johnston, who brought on 20-year-old Conor Brennan, who arrived from Leicester City during the summer, at half-time.
"He's been fantastic since he came in at the start of the season, but young Conor came in and did fantastically as well."
United had arrived two points clear of Hamilton Academical at the top of the Scottish Premiership and having won their last five games against Kilmarnock.
But goals from Tope Obadeyi and Mark Connolly within three second-half minutes lifted Kilmarnock above Inverness Caledonian Thistle and Celtic into third place.
"They've got top players throughout their whole team, but we just showed what we're capable of and we've got to make sure we can do that week in, week out," said Johnston.
"Sammy Clingan and Jamie Hamill were fantastic in the middle of the park.
"They totally dominated the middle area and you had Josh Magennis, who was causing all sorts of problems up front for them."
Johnston was also pleased with his side's movement off the ball, crossing and creation of chances.
"Obviously it was good to get the goals as well," he said. "We deserved them, but we defended really well as well."
Asked if Kilmarnock could maintain their recent good form, the Kilmarnock manager added: "It is going to be tough, but we've got the quality of players, so I'm sure if we work the way did today and the way we have the last few games, we'll not be far away.
"We can't get complacent. We must remember the hard work that's got us here."