The Canadian-born Dutch player joined the Spanish club before the close of Wednesday’s transfer deadline in a deal reported to be worth $11.4 million.
De Guzman scored five goals in 33 appearances for Mallorca last season and was a regular in coach Michael Laudrup’s starting lineup. He scored in Mallorca’s 1-0 opening round victory against Espanyol on Sunday.
De Guzman’s brother Julian, a Canada international, previously played in Spain for Deportivo La Coruna.
Villarreal, which was drawn against Bayern Munich, Manchester City and Napoli in the Champions League, opened the season with a 5-0 defeat to Barcelona.