3. Thomas Vermaelen
Having lost Rio Ferdinand and Nemanja Vidic this summer, United are determined to bolster their central defensive ranks.
Arsenal club captain Vermaelen, who was an unused substitute as Belgium beat Algeria 2-1 on Tuesday, is wanted at Old Trafford.
The Gunners are demanding £12m for the 28-year-old, who moved to the Emirates Stadium from Ajax in 2009.