The midfielder believes that the Brazilian playmaker is not interested in returning to the Bundesliga this summer, but reckons it will be hard for the club to buy him outright
The Brazilian playmaker moved to the Vicente Calderon on a season-long loan after falling out with Wolfsburg coach Felix Magath.
Diego has played an important role at the Spanish capital club, which has made Magath consider giving the 27-year-old another chance in the Bundesliga next season.
However, Juanfran says that Diego has his mind set on a permanent switch to Atletico and spoke of the importance of the club keeping their prized assets from leaving.
"If we keep this team and get one or two reinforcements, we will have a very competitive squad to play at the highest level," he said, according to AS.
"Diego wants to be here and wants to continue to be a player of Atletico. He feels the support of the fans and of the club, who made an important effort to sign him.
"But it does not depend only on him. Wolfsburg will want to get the best out of him, and we will try to make an effort for him."
Looking ahead to Wednesday's Europa League final against Athletic Bilbao, Juanfran was delighted to see the club reach the tournament decider and added that it will be a close match.
"One year and a half after I arrived at this club, I can win my first title and I want this match to come right away and of course to win it," the 27-year-old noted.
"The fans have to be proud because we are carrying the club's banner in Europe.
"We have joked about the final, saying we would have preferred to meet a foreign club, because this looks like a Primera Division or Copa del Rey match.
"We know each other very well and I am sure that this will be a very even match until the final minutes."