Rio Ferdinand has told the Sunday Times that Paul Pogba needs time to find his best form for Manchester United, and said he is confident the midfielder will justify his world-record transfer fee.

Pogba’s role in the team has been questioned due to a lack of goals or assists from midfield, but Ferdinand is confident the 23-year-old will become a key man for Jose Mourinho at Old Trafford.

“Paul is being criticised but he’s had an OK season at Old Trafford,” Ferdinand, who won six Premier League titles and the Champions League with United, said. “We’ve seen glimpses of what he can do. It’s now about him putting it together consistently, over 90 minutes and a whole campaign. I’m certain that will come.

“Pogba is hammered for not defending and not scoring enough. United didn’t buy him to be a defender or to score 30 goals a season. They bought him on his form for Juventus, where he had a loose, almost free role in a three-man midfield. United invested in a creative player, somebody to come in, make chances and be the dictator of the team.

“I agree with those who say that for £90m you need to see more but I’m confident he will get there. The team around him is still coming together. I see a progression. They’re playing football their supporters want to see, but Jose Mourinho knows there’s some shuffling of the pack and investing to be done, players to get out and others to bring in. Only after the next transfer window can we say this is a Mourinho squad.”

Ferdinand blamed United’s failure to challenge for the Premier League title on a lack of “killer instinct” and said Mourinho must add to the club’s attacking options at the end of the season.

“The first thing Mourinho must address is killer instinct,” Ferdinand added. “He needs somebody other than Zlatan Ibrahimovic to decide matches … I’d love to see Antoine Griezmann at Old Trafford. For four years running he’s scored 20-plus goals for Atletico Madrid in Spain and has genuine class and ability.”

The former defender expects Mourinho to strengthen other areas as well, with midfield another priority.

“Previous Mourinho teams contained powerhouses, guys who dominate physically,” Ferdinand said. “I see him going for that type in midfield, and United are linked with Monaco’s Tiemoue Bakayoko. His midfield partner, Fabinho, is very good too.

“Carrick can continue having a influence but he’s 36 this summer and United need someone else who can dictate from deep. The types I’d go for are Toni Kroos and Luka Modric, but you’re not going to prise them from Real Madrid. I like Adrien Rabiot at Paris Saint-Germain, and Saul Niguez of Atletico Madrid is another candidate. These are top players and will cost an arm and a leg.

“I admire Douglas Costa of Bayern Munich. He’s an electric player with pedigree who is not always in Bayern’s starting line-up and he’d be worth paying big money for. United have always played with wingers and you’ve got Ibrahimovic to feed in the air But most of all, the team needs legs.”