The Costa Rica international, who played 32 times for the Whites last season, has signed a contract that includes a £43m buyout clause.
Ruiz joined the Cottagers from Dutch outfit FC Twente in 2011 for £10.6m, scoring 13 times in 106 appearances during his time in England.
The 29-year-old almost joined Levante on loan back in February but the move fell through.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| C | Sporting Lisbon | 33 | 28 | 3 | 2 | 93 | 29 | 64 | 87 |
| 2 | Benfica | 33 | 25 | 4 | 4 | 76 | 27 | 49 | 79 |
| 3 | Porto | 33 | 21 | 6 | 6 | 62 | 27 | 35 | 69 |
| 4 | Braga | 33 | 21 | 5 | 7 | 71 | 49 | 22 | 68 |
| 5 | Vitoria de GuimaraesGuimaraes | 33 | 18 | 6 | 9 | 49 | 37 | 12 | 60 |
| 6 | MoreirenseMoreirense | 33 | 15 | 7 | 11 | 34 | 34 | 0 | 52 |
| 7 | AroucaArouca | 33 | 13 | 7 | 13 | 53 | 47 | 6 | 46 |
| 8 | FamalicaoFamalicao | 33 | 10 | 12 | 11 | 36 | 39 | -3 | 42 |
| 9 | SC FarenseFarense | 33 | 10 | 7 | 16 | 45 | 48 | -3 | 37 |
| 10 | Rio AveRio Ave | 33 | 6 | 18 | 9 | 37 | 42 | -5 | 36 |
| 11 | Gil Vicente | 33 | 9 | 9 | 15 | 42 | 51 | -9 | 36 |
| 12 | Casa Pia | 33 | 9 | 8 | 16 | 36 | 49 | -13 | 35 |
| 13 | Estoril PraiaEstoril | 33 | 9 | 6 | 18 | 48 | 56 | -8 | 33 |
| 14 | BoavistaBoavista | 33 | 7 | 10 | 16 | 37 | 60 | -23 | 31 |
| 15 | Estrela Amadora | 33 | 6 | 12 | 15 | 32 | 53 | -21 | 30 |
| 16 | PortimonensePortimonense | 33 | 7 | 8 | 18 | 36 | 71 | -35 | 29 |
| R | Vizela | 33 | 5 | 10 | 18 | 34 | 64 | -30 | 25 |
| R | ChavesChaves | 33 | 5 | 8 | 20 | 31 | 69 | -38 | 23 |
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