The 26-year-old impressed for the Yellow Submarine on a season-long loan last season, and coach Marcelinho has made the move permanent.
The former Spain Under-21 defender was signed for a fee in the region of £2.5m, according to Spanish publication AS.
Ruiz represents the club's fifth signing of the summer, following Samuel Garcia, Leo Baptistao, Alphonse Areola and Samu Castillejo.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Barcelona | 12 | 11 | 0 | 1 | 40 | 11 | 29 | 33 |
| 2 | Real Madrid | 11 | 7 | 3 | 1 | 21 | 11 | 10 | 24 |
| 3 | Atletico MadridAtletico | 12 | 6 | 5 | 1 | 18 | 7 | 11 | 23 |
| 4 | Villarreal | 11 | 6 | 3 | 2 | 20 | 19 | 1 | 21 |
| 5 | Osasuna | 12 | 6 | 3 | 3 | 17 | 16 | 1 | 21 |
| 6 | Athletic Bilbao | 12 | 5 | 4 | 3 | 18 | 12 | 6 | 19 |
| 7 | Real BetisBetis | 12 | 5 | 4 | 3 | 12 | 10 | 2 | 19 |
| 8 | Mallorca | 12 | 5 | 3 | 4 | 10 | 9 | 1 | 18 |
| 9 | Rayo Vallecano | 11 | 4 | 4 | 3 | 12 | 10 | 2 | 16 |
| 10 | Celta Vigo | 12 | 5 | 1 | 6 | 18 | 20 | -2 | 16 |
| 11 | Real Sociedad | 12 | 4 | 3 | 5 | 10 | 10 | 0 | 15 |
| 12 | GironaGirona | 12 | 4 | 3 | 5 | 15 | 17 | -2 | 15 |
| 13 | Sevilla | 12 | 4 | 3 | 5 | 12 | 17 | -5 | 15 |
| 14 | AlavesAlaves | 12 | 4 | 1 | 7 | 14 | 19 | -5 | 13 |
| 15 | Leganes | 12 | 2 | 5 | 5 | 12 | 16 | -4 | 11 |
| 16 | Getafe | 12 | 1 | 7 | 4 | 8 | 10 | -2 | 10 |
| 17 | Espanyol | 12 | 3 | 1 | 8 | 11 | 22 | -11 | 10 |
| 18 | Las PalmasLas Palmas | 12 | 2 | 3 | 7 | 13 | 21 | -8 | 9 |
| 19 | Real ValladolidValladolid | 12 | 2 | 2 | 8 | 9 | 24 | -15 | 8 |
| 20 | Valencia | 11 | 1 | 4 | 6 | 8 | 17 | -9 | 7 |
| > La Liga Full Table | |||||||||
