The 33-year-old Brazilian is surplus to requirements at Loftus Road with Rangers still keen to trim their wage bill following last season's relegation.
But with Monday's transfer deadline looming, Redknapp faces having an expensive player on the bench for the season behind current number one Robert Green.
"He's a fantastic goalkeeper, and that's not just a sales pitch to try to move him on," said Redknapp.
"He's an amazing professional and a great guy. He's a goalkeeper for any big club in the world; he's the Brazilian number one, he's got every medal there is to win.
"I just can't believe one of the big clubs in the world have not come in and taken him.
"Rob has been excellent for us and we've got Brian Murphy, who's a good keeper as well, so we are very lucky on that front."