Bayern Munich have apologised to club sponsor Adidas after Mario Gotze turned up wearing a t-shirt with a big Nike logo at his official unveiling on Tuesday.The Germany international joined Bayern from Borussia Dortmund this summer for a transfer fee of €37 million, but Gotze did not make a good first impression on one of his new club's main sponsors."The images from the press conference with Mario Gotze were a negative surprise to us. This is obviously unacceptable contractually as this was an official event of Adidas partners Bayern," a spokesperson for the company told Bild.Tuesday's events quickly prompted Bayern to contact Adidas and offer their apologies for the incident."We have apologised to Adidas on the phone. We have promised them that such a thing will never happen again," Bayern press officer Markus Horwick said.Adidas is the long-standing kit supplier to Bayern and owns a stake of around nine per cent in the Champions League winners.