Ron Vlaar
Probably the least likely of the lot in terms of age, but Vlaar has looked good in a lot of games for a struggling Aston Villa side. Although he might be close to 30 years old, the Dutch defender had earlier been linked with Manchester United at various times this season and signing the defender at a cut price next season might be one small step into fixing a defence that might have kept the goals out but has not looked stable at all.
Vlaar has worked with Louis Van Gaal earlier and knows what the boss would want, but something similar was said about Robin Van Persie and that has not worked out so well for either Van Persie or Van Gaal.
Whatever happens, the summer will be a crazy one for Manchester United with a slew of players coming in and quite a few going out.