TalkSport reports that Diarra has been told he can leave Real Madrid this summer after failing to make any major impact at the club.
Redknapp is keen to bring in a defensive midfielder and has also been linked with a move for West Ham star Scott Parker.
Diarra played under Redknapp at Portsmouth, who he left for Real Madrid in a £20million deal.
Spurs could face competition from Manchester United for the midfielder.
