Diego has urged Arda Turan to ignore any temptation to leave Atletico Madrid this January and continue his contribution to the club.
The Brazilian spent the 2011-12 season on loan at los Colchoneros, scoring three times in 30 La Liga appearances, and, in an interview with AS, was in no doubt of the importance of Turan to the side.
"He's playing perfectly," said the 27-year-old midfielder.
"He's a very creative player, of which there are many. Arda should continue at Atletico. If he leaves, I think he would be making a mistake."
Diego also spoke fondly of his time in the Spanish capital last season and praised los Rojiblancos' performances so far this campaign which have seen them occupy second place in La Liga, seven points clear of Real Madrid.
"The team are doing phenomenally this season. They are outdoing almost all their rivals in the league standings and should continue to do things well."
The Brazilian was also very clear about his own future at Wolfsburg where he has scored six times so far this campaign.
"My only reality is my club, Wolfsburg," he added.
"I've heard things about an alleged Galatasaray interest in me, but I cannot think of a transfer during this window.
"I have a contract with Wolfsburg and this is where I belong."