The former Blackburn centre-back is one of the west Londoners' key targets on transfer deadline day as the Rs boss looks to shore up his defence. Samba now looks set to leave Russian side Anzhi Makhachkala for Loftus Road after QPR on Wednesday triggered his release clause.
Press Association Sport understands personal terms still need ironing out but Rs boss Redknapp is confident a deal is close, and he told Sky Sports News: "I am not sure at the moment who we are signing. Samba has signed and that is a massive signing for us. That is the key one. He has passed his medical. He was having that last night so it shouldn't be a problem."
Samba is one of a number of players on Redknapp's radar.
The QPR boss is looking at bringing in another striker, with Stoke's Peter Crouch and West Brom's Peter Odemwingie amongst those targeted.
Redknapp is also looking to former club Tottenham for additions, with interest in Jermaine Jenas and David Bentley.
"It was difficult for David at Tottenham as I had Aaron Lennon and Gareth Bale," he said.
"It was a bit difficult for him to get in the side but we will have to wait and see. I am not sure what is happening with that one yet today.
"If Jenas is fit, he is a good player. We will have to wait and see."