New signing Geert de Vlieger has been ruled out of action so the City boss is already looking for cover for David James.
But a series of knocks to defenders, causing Keegan to thrust his youngsters into recent friendlies, has highlighted the fragility of his squad.
He told the City website: "I have told the Chairman that we don't have enough players at this football club. I am a bit short and had to use players for longer than I wanted to against Reading.
"We have asked a lot early in the pre season of a few players. We haven't had enough people. We haven't seen Trevor Sinclair yet. That was Nicolas Anelka's first game so it has been left to a few players to do a lot of work.
"The chairman's told me to go and get a couple of players but I have no money. I'm looking for really good players who can perform in the Premiership and take the team on who are Bosmans. That is not easy."
Keegan has managed to bring in Ben Thatcher this summer on a cut price deal but feels he needs to find another left-sided player soon, as well as a keeper.
However, Keegan praised the players that have come in recently, saying: "It's frustrating but what I'm pleased about is the way the players have responded and really pulled together."