The Super Hoops boss made nine changes to his team which drew 1-1 with West Ham United in the Premier League, but they put in a poor showing at Loftus Road as the visitors, under the guidance of Karl Robinson, took full advantage.
And Redknapp was annoyed that fixture congestion meant he had to shuffle his pack more than he would have liked.
“They’re getting older and you have to protect them because if they get injured I can’t replace these players. I haven’t got strength in depth for people to come in and play in these games.
“It’s very difficult. If I’ve got a squad here where I can drop and leave them out and bring another fantastic centre-half in or a fantastic midfield player then you do it but I had to do what I did.
“Today I played players that should be capable of beating a team from two divisions below.
“We need to strengthen. We’re trying. We’re only going to get weaker this week as Ryan Nelsen goes, it leaves us very short.
“Unless we get a few players in it’s going to be very difficult.”