Best, sustained a foot injury during City's 2-1 win against Ipswich Town yesterday and left the ground with a cast on his foot.
He was the only absentee from a 24 man squad, which included City keeper Keiren Westwood, that trained at Tipperary Town's Cooke Park this morning.
"It's the first time we've had very few cry-offs. Leon Best is a doubt; he's having an examination at Coventry today (on a foot injury) and they're going to let us know if he's available but I have to say it's doubtful. We've still got 23 players all happy to be here," said Liam Brady to the Republic Of Ireland website.