Unless Micah Richards recovers from a hamstring injury that kept him out at The Hawthorns, Mancini will have only Pablo Zabaleta, Vincent Kompany and Kolo Toure available to face the only side left with a 100 per cent record.
Related ArticlesWest Bromwich Albion 2 Manchester City 1Chelsea 3 Newcastle United 4Scunthorpe 2 Manchester United 5Aston Villa 3 Blackburn Rovers 1Wigan Athletic 2 Preston North End 1Sport on television"We have big problems," he said. "I hope that Micah Richards can recover. If not I don't know who can play left-back."
The obvious inference is that should Richards miss out, Zabaleta will play on the right side and Manchester City would look for an alternative on the left flank.
That could either involve Adam Johnson being pressed into emergency service, or more likely a midfield such as James Milner or Gareth Barry.
Either way, further injury fears shaped Mancini's team selection at The Hawthorns where, having taking a first-half lead through Jo, City were undone by two goals in as many minutes from Gianni Zuiverloon and Simon Cox.
"We couldn't take any risks," he said. "If I had more players available it would be a different team.
"But when you play like us and Chelsea, on Saturday at 12.45, the time to recover is very short.
"They would need minimum three days so to play tonight would have been dangerous."
It is to be hoped owner Sheikh Mansour understands the dilemma.
After spending £1 billion on City in just over two years, he was presumably hoping for an early end to the club's lengthy trophy drought.
That now cannot happen until May at the earliest, although Mancini has no regrets.
"I don't regret making the changes," he said. "Saturday is more important, the FA Cup is more important. The Europa League is more important.
"I did not regard this as a necessary sacrifice. We wanted to win. That is why I had four senior players on the bench.
"But I knew there was a chance we could lose because we started with six young players.
"I am happy with these guys. We might have lost the game but they can improve. If they do not play tonight, when will they ever play?"