"He is such a special player," said Redknapp. "He is out of the top drawer. You don't play in the French national team every game for the last 11 games if you are not a top player.
"I have worked up there with some good players and he is right up there with the best of them."
Diarra caused some consternation after he joined Pompey when he was quoted as saying he wanted to play for a big club in the future.
But rather than be disappointed by that attitude, Redknapp saw it as a positive.
"I think some players kiss the badge and say they love it and then as soon as they get an opportunity they disappear," he added.
"So what. Surely you have to be ambitious in this game haven't you?
"I don't see any problem with that if he comes here for the next few years and plays like he is playing - I will be delighted."