Diogo Dalot and Diogo Costa are team-mates for Portugal (Picture: Maisfutebol)

Diogo Dalot believes Manchester United transfer target Diogo Costa can become ‘one of the best goalkeepers in the world’.

Portugal international Costa has emerged as a target for United as Erik ten Hag searches for David de Gea’s long-term replacement.

De Gea, 32, has been at Old Trafford for more than a decade but appears to be on the decline and was slammed for the howler he made in Manchester United’s disappointing Premier League defeat to West Ham.

Ten Hag wants De Gea to sign a contract extension but cannot assure the Spaniard that he will remain United’s No. 1 as he looks at the likes of Costa, David Raya and Andre Onana.

Manchester United defender Dalot and Porto goalkeeper Costa are team-mates for Portugal and the Red Devils star has heaped praise on the Ten Hag target.

Costa has enjoyed an impressive season for Liga Portugal challengers Porto, keeping 19 clean sheets in 38 matches.

‘I grew up with him and he’s my friend, there’s a great relationship between us,’ Dalot told Maisfutebol.

Manchester United have expressed interest in the Porto goalkeeper (Picture: Getty)

‘I know perfectly well that he has the capacity to one day be one of the best in the world.

‘I don’t know if he’ll be at Manchester United or another big club in Europe, but he shows at Porto that he is a big player and has helped the club a lot.

‘If he continues there, I’ll be happy. If he leaves, I hope he has the greatest success at his next club.’

As well as signing a new goalkeeper this summer, Ten Hag wants to welcome a new midfielder and striker to Old Trafford as he looks to build on a promising first season in Manchester.