The Spaniard has given a predictable name as his answer.
The Real Madrid star left Old Trafford for the Bernabeu in 2009 but has been heavily linked with a move back to England in recent months.
United signed Ronaldo's team-mate Angel Di Maria in a big-money move this summer, while also adding a number of other new recruits.
But De Gea admits there is one name he would love to see added next: Ronaldo, although he admits it will be 'difficult' to prise him away for Spain.
"Of course I would like Cristiano Ronaldo to come to Manchester United," De Gea told Goal.com. "But I think it's difficult."
Meanwhile, on Man United's season so far, the Spaniard says he is not surprised at the club's slow start but says they will 'fight' on after regaining a place in the top four seven games into the Premier League campaign.
"There are lots of new people, a new coach, new concepts. In the end, it is a process. The coach [Louis van Gaal] knows we will improve and slowly pull upward," he said.
"We're starting to win games now and, with time, we'll be there. We will fight.
"It is important to get into the Champions League with Manchester United, to be among the best in Europe. Hopefully we can win a title, too."