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 | |
| 1 | Sporting Lisbon | 8 | 8 | 0 | 0 | 27 | 2 | 25 | 24 |
| 2 | Porto | 7 | 6 | 0 | 1 | 16 | 3 | 13 | 18 |
| 3 | Benfica | 7 | 5 | 1 | 1 | 17 | 5 | 12 | 16 |
| 4 | Santa ClaraSanta Clara | 8 | 5 | 0 | 3 | 11 | 9 | 2 | 15 |
| 5 | Braga | 7 | 4 | 2 | 1 | 12 | 4 | 8 | 14 |
| 6 | FamalicaoFamalicao | 8 | 3 | 4 | 1 | 9 | 4 | 5 | 13 |
| 7 | Vitoria de GuimaraesGuimaraes | 7 | 4 | 1 | 2 | 7 | 6 | 1 | 13 |
| 8 | MoreirenseMoreirense | 8 | 3 | 2 | 3 | 10 | 11 | -1 | 11 |
| 9 | Gil Vicente | 8 | 2 | 4 | 2 | 10 | 12 | -2 | 10 |
| 10 | AVS | 8 | 2 | 3 | 3 | 7 | 11 | -4 | 9 |
| 11 | Casa Pia | 8 | 2 | 2 | 4 | 6 | 11 | -5 | 8 |
| 12 | Rio AveRio Ave | 8 | 2 | 2 | 4 | 6 | 13 | -7 | 8 |
| 13 | AroucaArouca | 8 | 2 | 1 | 5 | 4 | 13 | -9 | 7 |
| 14 | Estoril PraiaEstoril | 7 | 1 | 3 | 3 | 4 | 10 | -6 | 6 |
| 15 | BoavistaBoavista | 7 | 1 | 2 | 4 | 3 | 8 | -5 | 5 |
| 16 | Estrela Amadora | 8 | 1 | 2 | 5 | 5 | 13 | -8 | 5 |
| 17 | Nacional | 7 | 1 | 2 | 4 | 4 | 12 | -8 | 5 |
| 18 | SC FarenseFarense | 7 | 0 | 1 | 6 | 2 | 13 | -11 | 1 |
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