Blues welcome Bolton to St Andrew's on Saturday in what is being dubbed as a must win game given the club's current position inside the relegation zone.
Since beating Arsenal in the final of the Carling Cup at the end of February Birmingham haven't managed to win a Premier League game and their poor form has seen them slip deeper into the relegation battle.
Having had two weeks away from the domestic action, McLeish hopes his players will return from the international break refreshed and ready for the impending fight to survive.
"We have had a bit of a beast since the cup final," the manager told the Birmingham Mail. "It is clear that often after a huge game like we had there is a reaction.
"It's not unique because as a club you have to dig deep into the reserves of energy in your players. But the fact is we lost momentum and need to get it back.
"It can't be a case of 'don't judge me on this game, judge me on the next one'. We haven't got that luxury."