The 23-year-old graduate of the Barcelona youth academy signed for Spurs in 2008 but had found his opportunities limited and had loan spells with Ipswich Town, Galatasaray and Racing Santander.
Dos Santos helped Mexico win gold at the Olympic Games in London.
Mallorca are sixth in La Liga after a win and a draw from their opening two matches.
Meanwhile, Celta Vigo have agreed to sign South Korea striker Park Chu-young on loan from Arsenal for the season.
The 27-year-old made six appearances for Arsenal last season, scoring once, after joining from AS Monaco last year.
Park played in the 2006 and 2010 World Cups and helped his country to a bronze medal at the London Olympics, where he scored two goals.
Celta have lost their opening two matches on their return to La Liga this season.
- Celta Vigo
- La Liga
- Ipswich Town