The 19-year-old announced last month that he would be leaving the San Siro this summer.
The Premier League trio have now stepped up their pursuit for the Dutchman, according to insidefutbol.com.
Castaignos, who has four years left on his contract, scored one goal in six appearances for the Nerazzuri last season.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| C | Inter Milan | 35 | 28 | 5 | 2 | 81 | 19 | 62 | 89 |
| 2 | AC Milan | 35 | 21 | 8 | 6 | 67 | 42 | 25 | 71 |
| 3 | Juventus | 35 | 18 | 12 | 5 | 48 | 27 | 21 | 66 |
| 4 | Bologna | 35 | 17 | 13 | 5 | 49 | 27 | 22 | 64 |
| 5 | Atalanta BCAtalanta | 34 | 18 | 6 | 10 | 63 | 38 | 25 | 60 |
| 6 | Roma | 35 | 17 | 9 | 9 | 62 | 42 | 20 | 60 |
| 7 | Lazio | 35 | 17 | 5 | 13 | 45 | 37 | 8 | 56 |
| 8 | Napoli | 35 | 13 | 12 | 10 | 53 | 44 | 9 | 51 |
| 9 | Fiorentina | 34 | 14 | 8 | 12 | 51 | 39 | 12 | 50 |
| 10 | Torino | 35 | 11 | 14 | 10 | 31 | 31 | 0 | 47 |
| 11 | Monza | 35 | 11 | 12 | 12 | 38 | 46 | -8 | 45 |
| 12 | Genoa | 35 | 10 | 13 | 12 | 41 | 43 | -2 | 43 |
| 13 | Lecce | 35 | 8 | 13 | 14 | 32 | 50 | -18 | 37 |
| 14 | Hellas VeronaHellas Verona | 35 | 8 | 10 | 17 | 33 | 46 | -13 | 34 |
| 15 | CagliariCagliari | 35 | 7 | 12 | 16 | 37 | 60 | -23 | 33 |
| 16 | FrosinoneFrosinone | 35 | 7 | 11 | 17 | 43 | 63 | -20 | 32 |
| 17 | Empoli | 35 | 8 | 8 | 19 | 26 | 50 | -24 | 32 |
| 18 | Udinese | 35 | 4 | 18 | 13 | 33 | 52 | -19 | 30 |
| 19 | SassuoloSassuolo | 35 | 7 | 8 | 20 | 41 | 70 | -29 | 29 |
| R | Salernitana | 35 | 2 | 9 | 24 | 27 | 75 | -48 | 15 |
| > Serie A Full Table | |||||||||
