Kilmarnock 1-2 Rangers: Sweat over stricken Martyn Waghorn
Rangers' top scorer, Martyn Waghorn, left Rugby Park on crutches after his side's Scottish Cup win over Kilmarnock.
The Englishman suffered an injury winning an early penalty and, though he took - and scored - the spot kick, played no further part in the game.
Rangers boss Mark Warburton said: "With Martyn, it was one of those ones where he locked legs as he fell.
"He has an abrasion on his knee. He took the penalty, credit to him, but we will see how he is in the morning."
Nicky Clark's stoppage-time strike gave Rangers a 2-1 victory and a quarter-final tie with either Dumbarton or Dundee.
The penalty was Waghorn's 28th goal of the season and gave Warburton a first win over a top-flight side having been beaten by St Johnstone in an October League Cup tie ahead of drawing the original Ibrox fixture with Kilmarnock.
"Whether you beat a Northern Premier League team or a Premier League side, you still go through or go out, it doesn't matter who you play," he said.
"I felt we should have got a result at Ibrox, but we had 9,000 fans here and had a responsibility to come and deliver the result."
Kilmarnock assistant manager Lee McCulloch bemoaned "criminal" lapses in concentration from his side that led to both Rangers goals.
"A lapse in concentration the first minute gave away a clear penalty," said the former Ibrox player. "We showed great character to come back into the game.
"Usually this season, if we've gone one down, we collapse and lose four or five.
"We showed great character, scored a great goal then a lapse in concentration in the last minute has cost us.
"I think the last 25 minutes Rangers really dominated, created chances and probably overall deserve to go through."