Manchester United have completed the signing of Athletic Bilbao midfielder Ander Herrera.The Old Trafford club have confirmed that the 24-year-old has agreed a four-year deal and, in doing so, becomes new manager Louis van Gaal's first signing at Old Trafford.Earlier on Thursday Athletic announced that the midfielder had paid his buyout clause, paving the way for him to move to England after the Basque club had previously rejected a £29 million offer.And, having now been announced as a new Manchester United player, Herrera insists he cannot wait to play his first game for the Red Devils. He told the club's official website: "Signing for Manchester United is a dream come true. "I have played at Old Trafford for Athletic Club in the Uefa Europa League and it was one of the highlights of my career so far. I have joined United to do all I can to help the team reach the club's objectives. "Having arrived on Tuesday, I'm excited to now be living in Manchester and I can't wait for my first game in United's famous red shirt. "I will never forget my time with Athletic Club and I'd like to thank the fans and staff for all their support and, above all, wish all my fantastic former team-mates all the best for the future."United assistant Ryan Giggs added: "Ander is a fantastic young player, with great energy and creativity. We believe him to be one of the brightest young prospects in Spain and I am certain he will be a big hit with the United fans. "I'm delighted he has made the decision to come to Manchester and play his part in the club's future. I'm looking forward to seeing him in action on our summer tour to America."