The Spanish youngster, who claimed his first WTCC victory earlier this year at Marrakech, will race in a Chevrolet Cruze run by the Tuenti Racing Team with RML technical support from Porto onwards.
“We had a good offer from RML to run with one of their cars and decided to accept it," the driver said.
"I am grateful to SEAT, who have given me the opportunity to build my professional racing career since when I was 15 in the León Supercópa up to the WTCC.
"I would love to stay with them, but so far they have not decided about future programmes. I have to think about myself and I could not let the opportunity to drive a Chevrolet pass.
“We won’t have the time for a proper test before Porto, so we have just planned a shakedown somewhere in England."
The Porto weekend is on June 29-30, with five further events in 2013.