The Barcelona midfielder snubbed a move to Old Trafford last summer but the Spain goalkeeper has not given up hope of convincing the 27-year-old to make the switch to England
Fabregas's future at Camp Nou is uncertain following a difficult 2013-14 campaign for the Catalan club, with new boss Luis Enrique refusing to confirm the Spain international will definitely stay put for next season.
United openly pursued the former Arsenal captain last summer only for the midfielder to reject a move to England, but with the 27-year-old a potential target for new United boss Louis van Gaal, De Gea insists he is trying to get his compatriot to return to the Premier League.
When asked about Fabregas, De Gea told La Sexta: "I've tried to convince Cesc to join United but it's difficult. He feels great at Barca, it's his home."
Former Atletico Madrid goalkeeper De Gea could win his first cap for Spain in their World Cup warm-up fixture against Bolivia on Friday and insists he cannot wait to be given the chance to make his first appearance for his country.
"We don't know who's going to play against Bolivia, but we have to be ready in case we get the nod," he said.
"I'm raring to make my debut. There's a lot of competition in goal, but I'm enjoying myself and pushing myself to the max in training.
"There's a lot of speculation about who will go to Brazil and who won't. A few players are carrying fitness issues and we just have to wait for the gaffer to make his decision: it's as simple as that."
Vicente del Bosque has delayed announcing his final 23-man squad for the tournament in Brazil partly due injury concerns around Chelsea-bound Diego Costa and De Gea agrees that the Atletico striker should be given us much time as possible to recover.
"Of course we should wait for Costa, he's a top player. I played alongside him for several years at Atleti and he's really blossomed this year.
"We have to wait and see how he progresses and hopefully he'll be 100 per cent."