The Serbian midfielder joins the club for €11m (£9.4m) with another €4m (£3.4m) to be paid in add-ons.
The 21-year-old met his new teammates for a training session soon after completing the move on Wednesday.
Ljajic leaves Fiorentina after three years at the Stadio Artemio Franchi.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Napoli | 21 | 16 | 2 | 3 | 35 | 14 | 21 | 50 |
| 2 | Inter Milan | 20 | 14 | 5 | 1 | 51 | 18 | 33 | 47 |
| 3 | Atalanta BCAtalanta | 21 | 13 | 4 | 4 | 46 | 24 | 22 | 43 |
| 4 | Lazio | 21 | 12 | 3 | 6 | 37 | 28 | 9 | 39 |
| 5 | Juventus | 21 | 8 | 13 | 0 | 34 | 17 | 17 | 37 |
| 6 | Fiorentina | 20 | 9 | 6 | 5 | 33 | 21 | 12 | 33 |
| 7 | Bologna | 20 | 8 | 9 | 3 | 32 | 26 | 6 | 33 |
| 8 | AC Milan | 20 | 8 | 7 | 5 | 29 | 21 | 8 | 31 |
| 9 | Roma | 21 | 7 | 6 | 8 | 31 | 27 | 4 | 27 |
| 10 | Udinese | 21 | 7 | 5 | 9 | 24 | 32 | -8 | 26 |
| 11 | Torino | 21 | 5 | 8 | 8 | 21 | 26 | -5 | 23 |
| 12 | Genoa | 21 | 5 | 8 | 8 | 18 | 30 | -12 | 23 |
| 13 | Como | 21 | 5 | 7 | 9 | 26 | 34 | -8 | 22 |
| 14 | CagliariCagliari | 21 | 5 | 6 | 10 | 23 | 34 | -11 | 21 |
| 15 | Empoli | 21 | 4 | 8 | 9 | 20 | 28 | -8 | 20 |
| 16 | Parma | 21 | 4 | 8 | 9 | 26 | 36 | -10 | 20 |
| 17 | Lecce | 21 | 5 | 5 | 11 | 15 | 36 | -21 | 20 |
| 18 | Hellas VeronaHellas Verona | 21 | 6 | 1 | 14 | 24 | 47 | -23 | 19 |
| 19 | VeneziaVenezia | 21 | 3 | 6 | 12 | 19 | 34 | -15 | 15 |
| 20 | Monza | 21 | 2 | 7 | 12 | 20 | 31 | -11 | 13 |
| > Serie A Full Table | |||||||||
