The Juventus midfielder is believed to be close to returning to Old Trafford in a world-record deal in excess of £100million which Ferdinand has backed.
The former centre-back played with the Frenchman during his initial spell at United and feels it is vital that a deal is done for the good of the mindset of the Red Devils playing group.
Ferdinand recalled an interaction with Pogba when the 23-year-old left Manchester for Juventus in 2012.
He said via BT Sport: “When he left, I said: 'Why are you leaving?'. He said: 'I want to be the best player in the world.'
“Those were his words to me. And he's on the right track. He's not there yet.
“If he doesn't sign, it could have an adverse effect mentally on the players in the dressing room for a short period of time. It's important they sign him."