Mamadou Sakho ended a tumultuous spell at Liverpool by completing a season-long loan to Crystal Palace last night.
The central defender was a key member of Jurgen Klopp's back four when the German boss first came in.
But Sakho fell out with the Liverpool boss in a pre-season tour of America in the summer and has not featured for the first team this season.
Mamadou Sakho has joined Crystal Palace on a season-long loan
Rio Ferdinand believes Mamadou Sakho is Liverpool's best defender
His career at Anfield now looks over having moved to Selhurst Park with Liverpool hoping to recoup most of the £20million they spent on him come the summer.
But Ferdinand believes Liverpool have let their best defender leave at a time when they need stability the most.
"I think he's Liverpool's best defender if he's fit and available to play," Ferdinand told BT Sport.
Mamadou Sakho scores for Liverpool U23s in pictures
Sun, November 20, 2016
Click through the gallery for the best snaps of Mamadou Sakho scoring for Liverpool U23s
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Click through the gallery for the best snaps of Mamadou Sakho in action
"Last season he was very good and I think they've missed him this season.
"He was their leader at the back. He's athletic and he'll be a great addition to Crystal Palace."