But the Blues boss still intends to put out a strong side for the Premier League finale.
David James, Sulley Muntari, John Utaka and Pedro Mendes are all in the frame for a return to the squad on Sunday.
The quartet all missed the defeat to Middlesbrough but this week returned to training.
Redknapp and his medical staff must now assess whether it is wise to grant them an instant recall.
With eight days to go until the FA Cup final, he is only too aware the wrong choice could rule out one of his key performers.
Whatever his decision, a strong Pompey side will take on a Fulham side fighting for their Premier League lives.
That will include Jermain Defoe – who is cup-tied for the final – while Kanu is recalled to the squad having been rested last weekend.
However, David Nugent, who tweaked his groin warming-up for the reserves on Tuesday night, will not be risked.
Redknapp said: 'I don't want anyone playing who is not 100-per-cent fit. That's not a chance I can afford to take.
'I couldn't risk David James if he was not right.
'He will want to play but if he does his calf may go, it's too big a gamble.
'John Utaka still has a little bit of a problem with his ankle, there is still swelling around it, so he's another.
'It's not that I don't want to risk them, if they are not fit they are not fit so I can't play them.
'Jamie Ashdown can come in for Jamo and he's done okay, he's done nothing wrong. There will still be a strong side, it's not about resting anyone for the final.
'I wouldn't do that, that's not really on.
'If they are fit they will play – if they are not fit they will not play. We have got to wait and see.'
Redknapp will field his favoured home formation of 4-4-2 and has revealed he will give both Kanu and Milan Baros the chance of a precious pre-Wembley run out.
He added: 'The problem is we need to get games into other people. I will play Defoe and also want to give Kanu and Milan a game, perhaps I can give them half a game each.
'I have only got three strikers for the final and one of them may not be fit so I need to get the other two time on the pitch.'

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