The 22-year-old Spaniard was part of the Bilbao side that dumped United out of the Europa League last month.
Reds boss Sir Alex Ferguson is thought to have had the player scouted twice in recent weeks, according to The Mirror.
However, the Premier League champions may be reluctant to pay the £26m release clause in De Marcos's contract.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Manchester CityMan City | 4 | 4 | 0 | 0 | 11 | 3 | 8 | 12 |
| 2 | Arsenal | 4 | 3 | 1 | 0 | 6 | 1 | 5 | 10 |
| 3 | Newcastle UnitedNewcastle | 4 | 3 | 1 | 0 | 6 | 3 | 3 | 10 |
| 4 | Liverpool | 4 | 3 | 0 | 1 | 7 | 1 | 6 | 9 |
| 5 | Aston Villa | 4 | 3 | 0 | 1 | 7 | 6 | 1 | 9 |
| 6 | Brighton & Hove AlbionBrighton | 4 | 2 | 2 | 0 | 6 | 2 | 4 | 8 |
| 7 | Nottingham ForestNott'm Forest | 4 | 2 | 2 | 0 | 4 | 2 | 2 | 8 |
| 8 | Chelsea | 4 | 2 | 1 | 1 | 8 | 5 | 3 | 7 |
| 9 | Brentford | 4 | 2 | 0 | 2 | 6 | 6 | 0 | 6 |
| 10 | Manchester UnitedMan Utd | 4 | 2 | 0 | 2 | 5 | 5 | 0 | 6 |
| 11 | Bournemouth | 4 | 1 | 2 | 1 | 5 | 5 | 0 | 5 |
| 12 | Fulham | 4 | 1 | 2 | 1 | 4 | 4 | 0 | 5 |
| 13 | Tottenham HotspurSpurs | 4 | 1 | 1 | 2 | 6 | 4 | 2 | 4 |
| 14 | West Ham UnitedWest Ham | 4 | 1 | 1 | 2 | 5 | 6 | -1 | 4 |
| 15 | Leicester CityLeicester | 4 | 0 | 2 | 2 | 5 | 7 | -2 | 2 |
| 16 | Crystal Palace | 4 | 0 | 2 | 2 | 4 | 7 | -3 | 2 |
| 17 | Ipswich TownIpswich | 4 | 0 | 2 | 2 | 2 | 7 | -5 | 2 |
| 18 | Wolverhampton WanderersWolves | 4 | 0 | 1 | 3 | 4 | 11 | -7 | 1 |
| 19 | Southampton | 4 | 0 | 0 | 4 | 1 | 8 | -7 | 0 |
| 20 | Everton | 4 | 0 | 0 | 4 | 4 | 13 | -9 | 0 |
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