Villarreal have announced that ASISA will be the new official medical provider for Villarreal CF, for its employees, staff and players up to and including the first team. Interestingly, the press release says there was a mediator involved in the negotiations, which might be unusual--I don't know how these sorts of things usually go in Spain.
Sanitas had been providing medical services to the club for some time; I would guess the decision to change was made for purely financial reasons, as is typical here when shopping insurers. Asisa is the biggest health care company in Spain.
It sounds as though this takes effect immediately, but I guess we won't know until we see a stoppage and catch the logo on the back of the medicos' shirts!