Mircea Lucescu, coach of Douglas Costa's former club Shakhtar Donetsk, contradicted comments he made last week by saying that Costa is not yet good enough for Bayern Munich.
"I think Costa is not yet strong enough for Bayern. Ribery and Robben are a different caliber," Lucescu told Bild, although he added that Costa can improve. "He can grow and make it there."
Last week Lucescu had praised Costa's qualities, saying: "He is equally good with both feet, has a sense for free spaces, a strong shot and above all he is tremendously fast."
Costa was signed by Bayern for a reported fee of €30 million. He can play on both offensive wings. With Franck Ribery's return after his ankle injury still uncertain, Costa could step in for him at the start of the season.
"Costa is no substitute for Franck Ribery," FC Bayern sporting executive Matthias Sammer told Abendzeitung.
Pep Guardiola said he's confident that Costa will strengthen his squad.
"I thank the club for the signing of Diego Costa."
Costa is currently on holiday after playing for Brazil at the Copa America. He missed a penalty in Brazil's shootout defeat against Paraguay. He will start team training with Bayern Munich on July 11.