Roman Weidenfeller believes it would be detrimental for Borussia Dortmund team-mate Ilkay Gundogan to join Manchester United or Real Madrid.
The midfielder, 23, is a key cog in the Schwarzgelben first team and has been heavily linked with a move to the Red Devils or the Blancos.
However, BVB and Germany goalkeeper Weidenfeller thinks Gundogan's development as a player would suffer if he were to leave Signal Iduna Park in 2014.
"I would advise Gundogan to stay," he told Kicker. "His development is not yet over. There are a lot of challenges he can help us with at Dortmund."
With the Bundesliga winter break coming to an end, Weidenfeller is concentrated on his team's first game of the calendar year on Saturday and asssting his side's attempts to improve upon their current fourth place.
"We are fully prepared going into the game against Augsburg," added the 33-year-old. "It is crucial that we finish in a Champions League place and now we want to start catching up."
Jurgen Klopp's men trail leaders Bayern Munich by 12 points, second-placed Bayer Leverkusen by five points and Borussia Monchengladbach in third by a solitary point.