4. Iñigo Martínez
Martinez is emerging as one of the best young defenders in Spain. The 22-year-old has made 78 appearances for Real Sociedad since 2011 and has become an integral part of the team. The youngster played against Manchester United last year in the Champions League and certainly gave them a run for their money.
Martinez has a superb pace and is good in the air making him a potential candidate to replace Vidic who possesses similar qualities. A lot of club are pursuing the youngster but Manchester United have a good chance of capturing his signature.
The Spain international also has an eye for goal which can come in handy in tricky situations. The only disadvantage about Martinez is his knack for picking up red cards having already collected 2 so far.