A gruelling few days caught up with City in Sunday's defeat to Fulham, according to manager Mark Hughes.
With the UEFA Cup quarter final second leg looming this Thursday and injuries to contend with, the boss made several changes from the team that played in Hamburg three days ago, but the Blues were shocked by a second half comeback from Fulham that overturned Stephen Ireland's sublime 28th minute strike.
Hughes said, "Tiredness was a significant factor, we were missing key senior players today and we needed some energy because of a lot was expended on Thursday. We made a few changes to protect some other players as well with the next game coming up.
"I was reasonably satisfied with 1-0 at half-time, Fulham were quite prepared to get people behind the ball and make it difficult for us. Stevie's goal was a fantastic strike, and in the second half we looked to keep it solid.
"Every goal we conceded was a poor goal, and the second made it really difficult because the energy we had used up in midweek made chasing the game difficult. We just did not have enough left to affect the game and get up to the Fulham players, who were quite happy to keep possession and pick us off in the end. There were just too many of the team feeling the effects of a long season and a difficult week."
City mistakes led to each Fulham goal, and again the boss feels that City's European exertions took their toll.
"It might be a consequence of the tiredness we had, and tired players make mistakes. When you give the ball away in bad areas, teams will punish you very quickly."
Robinho was rested with an eye on Hamburg's visit, Martin Petrov making his long-awaited comeback, as Hughes observed, "It was the first opportunity I have had to give Robbie a break, and I had the option of Martin who needed to get involved again. It was a young side at the end, and we need senior players to get back for us on Thursday."
There is also mixed news on the injury front, the boss concluding with:
"We're hopeful that Shaun Wright-Phillips will be OK, Wayne Bridge is a doubt but could be a possible - we'll have to wait and see. Craig Bellamy is being assessed early in the week and is out, and Vincent Kompany is touch-and-go."