United have been unsuccessful with two bids for the Barcelona midfielder and are reportedly set to make a third offer of £40m.
"He will have to make the decision whether he wants to stay or join us," De Gea told the Manchester Evening News. "It would be a very good signing and he would help us improve greatly."
De Gea was unsuccessful in convincing Spanish U21 team-mate Thiago Alcantara to move to Old Trafford, the midfielder opting to join former coach Pep Guardiola at Bayern Munich.
But the 22-year-old insists that the Premier League remains the best in the world and wants more Spaniards to make the move to England.
"It's the best organised league," he said. "Everything is well organised on every level, even financially. You can see this. The players know it. It's a very attractive league and I like it a lot.
"The grounds are full so it's understandable that Spaniards should want to come here. It's important there are more Spaniards so that the Premier League is followed more in Spain.
"It's great that Spanish players are in England, it makes everything more fun. Hopefully players from our country keep going to England.
"I've been here for two years, I feel that I have a normal life. Also, I have family and friends who come over a lot. I am very settled."