Peter Bosz joked that Pierre-Emerick Aubameyang is a "terrible player" in an attempt to ward off interest from Real Madrid as Borussia Dortmund prepare for their Champions League clash at the Santiago Bernabeu.
Gabon striker Aubameyang has long been linked with the European champions, having spoken in the past of his desire to play for Los Blancos to fulfil a promise made to his Madrid-supporting grandfather.
His latest chance to impress up close comes on Wednesday as Dortmund take on Zinedine Zidane's men knowing it will be their last fixture in the Champions League this season, although they still require a win to guarantee passage to the Europa League.
A wretched run of form has seen Dortmund drop from Bundesliga leaders to sixth and put paid to their European hopes, but Bosz remained jovial when quizzed on Aubameyang's ability to play for Madrid in the future.
"He is a terrible player, very bad, not worth it for Real Madrid," Bosz told a news conference.
"It's a joke. I'm telling you that so he stays with us. He is excellent and has the quality to play for Real Madrid but I hope he stays here."
Bosz comes into the game under increasing pressure, with Dortmund's only win in their last 11 games coming in the DFB-Pokal against third-tier Magdeburg.
Opposite number Zidane has also come in for criticism with Madrid fourth in LaLiga, eight points adrift of table-topping Barcelona.
Bosz does not believe that Zidane ought to be so concerned, however.
"We are in a difficult phase, but must try to play a good match," he said. "It is not just a game for points, but also for confidence.
"If Real is in a crisis, then what are we?"