But is there anyone available who are superior to former Barcelona keeper Victor Valdes?
We take a look at five potential United No1's:
JASPER CILLESSEN (AJAX)
If there is a favourite to succeed De Gea at Old Trafford, it has to be Cillessen. Louis van Gaal took the Ajax keeper to the World Cup last summer and he has worked closely with United keeper coach Frans Hoek.
Cillessen first broke United's interest as early as February and admitted the chance to work with Hoek again was attractive. The 26 year-old has flirted with the Premier League in the past, coming close to joining Brendan Rodgers' Swansea City four years ago before leaving NEC Nijmegen for Ajax.
Former United keeper Rai van der Gouw is a fan and insists: "Manchester United will get a very good goalkeeper.
"The rumours been there for some time. The arrival of a Dutch goalkeeper is obvious."
FERNANDO MUSLERA (GALATASARAY)
The Uruguay international is being linked with United in this week's Turkish press. The 28 year-old was key to Gala's Super Lig title triumph this season, with local pundits rating him the biggest influence on the championship. Muslera kept five consecutive clean sheets - all of which ended in victories - at the most critical stage in the season.
United have followed Muslera since his time in Uruguay and kept tabs on his progress during four years at Lazio. Former United boss Sir Alex Ferguson is a fan and made an attempt for Muslera when doubts emerged over De Gea's long-term suitability to the Premier League.
Muslera, also linked with Arsenal, is well aware of English interest: "I dreamed as a child of the Premier League. It is probably a dream for every footballer to play in England."
HUGO LLORIS (TOTTENHAM)
Is the English media favourite to succeed De Gea. The Frenchman has stated he wants Champions League football, which is appearing more and more remote at White Hart Lane. But Spurs hold a strong hand, with Lloris having penned terms to 2019 only last July.
Talk of a buyout clause has been dismissed by Tottenham officials and if United do want to buy, they will have to pay over the odds to prise Lloris away. Former club Olympique Lyon will be due 20 per cent of any sell-on fee.
"You don't know what could happen. There is one important thing, there is a moment to think about yourself, to sit down and reflect," he said this week.
"But when that moment has passed and the season starts, you're fully committed to the club's project and to the team [you're with]."
MARC-ANDRE TER STEGEN (BARCELONA)
Is expected to start against Juventus tomorrow in the Champions League final, but could still seek a move away over the summer. Ter Stegen has been frozen out of La Liga action, with Barca coach Luis Enrique preferring Claudio Bravo.
The 23 year-old is among a wave of exciting, young German keepers, but fears being left behind if his progress continues to be restricted.
"My current situation is not easy for me.
"I have to be patient. I'm doing everything possible to prove myself in training and to make things difficult for the coach. I've had some good performances, but people always remember the bad times."
But he can count on teammate Lionel Messi as a big fan.
"Ter Stegen surprised me a lot from the first day," said the Barca icon. "He could be the best in the world in a few years."
ASMIR BEGOVIC (STOKE CITY)
But his form last season has created some doubts and talk of a big club move has begun to dry up. He sparked some controversy when refusing to sit on the bench as Stoke boss Mark Hughes handed Jack Butland a late season chance.
Hughes, however, remains a fan of Begovic, rated the best at Stoke since Gordon Banks.
"If Asmir stays we will continue to look to develop Jack and the likelihood is he would probably go out on loan again (he spent time with Sky Bet Championship side Derby earlier in the campaign), if the right club was available."