The sides will meet at Old Trafford on Thursday, and Athletic will be considered underdogs to the Premier League giants whose surprise participation in this competition follows an early exit from the Champions League. The Red Devils are widely considered as favourites to lift the trophy but the 19-year-old thinks his team can come out of Manchester with a positive result if United get complacent. \"Maybe they could be affected by relaxing too much, which can happen if you feel superior to your opponents,\" Muniain told Press Association Sport. \"We all know the high quality of their players, but sometimes subconsciously, you can relax too much and if we take advantage of that we can cause them some damage. \"It\'s a game we\'ve been looking forward to for a long time. We\'re going there with every intention of giving Manchester United a scare and getting a positive result for the return leg. \"If we can keep the tie alive from Old Trafford, San Mames will be up for a big European night [in the return leg].\" The young forward recently made his full debut for the Spanish national team in an international friendly win over Venezuela. He has been an integral part of Athletic\'s side this season helping them to the Copa del Rey final and scoring in both legs of their last-32 Europa League victory over Lokomotiv Moscow. His performances have not gone unnoticed as numerous Premier League teams are thought to be monitoring him, however, Muniain insists he wants to stay in La Liga. He added: \"No, right now I don\'t see it [himself in the Premier League]. \"I\'m not thinking about anything else than this great club, which is what I love most. But, as I\'ve said many times, in football you never know what can happen.”