Christopher Samba has passed his medical ahead of the proposed move from Russian side Anzhi to QPR after manager Harry Redknapp triggered Samba's £12.5m release clause.
Redknapp told Sky Sports News on Thursday morning: "Samba has signed and that's massive for us, that is they key one.
"He has passed his medical, he was having that last night so it shouldn't be a problem."
Samba could prove to be a vital signing for the Londoners, who have lost Ryan Nelsen, who has taken over the vacant managerial position at FC Toronto, and with QPR knee-deep in a relegation battle required additional defensive options having allowed Anton Ferdinand to leave the club for Turkish side Bursaspor.
The former Blackburn defender Samba has left Russia, with Anzhi manager Guus Hiddink confirming the departure of the Congolese powerhouse in the Mail.
"He left for England yesterday," he said. "I hope that today or tomorrow we'll find out what really happened.
"It's a shame to talk about this but he didn't even say goodbye, he didn't explain anything to us.
"It's not a great situation for us. He started the pre-season camps with us but then suddenly in the last few days he started to make contact with England, that's despite still being under contract with Anzhi," Hiddink said.
Former Tottenham manager Redknapp is also planning a swoop for past players, Jermaine Jenas and David Bentley, both who played for him under his reign at North London.
QPR have been one of the most active clubs this month, with Loic Remy, Tal Ben Haim and Yun Suk-young all arriving at Loftus Road, with Stoke striker Peter Crouch still being linked with a potential transfer deadline day move.
Meanwhile, QPR have also given Alejandro Fraulin permission to speak to Palermo over a potential loan move.