Athletic Club midfielder Ander Herrera is set to be sidelined for up to six weeks after undergoing an operation on a sports hernia. The 23-year-old, who was part of Spain\'s Olympic squad this summer, successfully went under the knife this morning in Munich after being ruled out of last weekend\'s La Liga win over Real Valladolid with the problem. A statement on Athletic\'s website read: \"If there are no complications in the post-op period, the player will be discharged on Saturday 8 September and will return to his home. The recovery period for this type of operation is between four and six weeks.\" FIFA