Northern Ireland are sweating on the fitness of Kyle Lafferty and Paddy McCourt ahead of Friday's meeting with Serbia.
Nigel Worthington's side entertain the White Eagles at Windsor Park in a crucial European Championship qualifier.
They go into the game knowing that a win could see them leapfrog second-placed Slovenia in Group C.
Celtic midfielder McCourt, who scored twice in the win over the Faroe Islands in August, and Rangers striker Lafferty are both struggling with calf injuries.
Worthington said: "Time is starting to catch up with them a little bit but we'll carry on working with them on a continuous basis and see where we're at.
"The injury situation with them is becoming a little bit difficult but we'll have to see."
"It's an unfortunate situation that the two boys have picked up these knocks and with 24 hours to go time is getting tight. At this moment in time it's all ifs, buts and maybes."
With Derby striker Jamie Ward also out of the 23-man squad, out-of-form David Healy could win a call-up to the starting line-up.
However, the Rangers striker has not played many games recently and has failed to score an international goal since October 2008.