Redknapp has several key players injured after the 6-0 mauling by Manchester City at the weekend, and at the start of a crucial few days.
“I am struggling to find enough players to put out a decent team,” he said.
“This game could not have come at a worse time. I always try to put out the best team I can, but this is an occasion when one or two players really will be thrown in at the deep end.”
Sol Campbell is among the experienced players who will be missing for the tie at Fratton Park. Also out are midfielders Lassana Diarra, Papa Bouba Diop and Sean Davis, as well as leading scorer Jermain Defoe.
Niko Kranjcar is still sidelined as he recovers from the injury he picked up earlier in the season.
Redknapp added: “After the Chelsea game we take on Tottenham at the weekend and then travel to Portugal for the
UEFA Cup second leg against Vitoria before coming back to play Stoke. It is a very hectic period, and I simply cannot afford to take any chances with players who have knocks.
“Playing Chelsea is hard enough at the best of times, but we will give it a real go and do our best.”
Glen Little is set for his Pompey debut following his summer move from Reading, and Richard Hughes and Kanu may make their first starts of the season following injury.