The 19-year-old, a Brazil-born Spain under-19 international, only joined the Portuguese club last month on a five-year deal from Real Madrid but he has moved to the Reebok Stadium to gain experience. He is reunited with former Real team-mate Marcos Alonso, who joined Bolton in July.
"He is a quick, exciting young player who can play up front and in wide positions," said Wanderers assistant manager Sandy Stewart.
Stewart added: "We watched Rodrigo play alongside Marcos in the Real Madrid B team last season and we were obviously interested in signing the two of them.
"He went to Benfica as part of the Angel di Maria deal but we still chased his signature and now we are delighted to eventually get him.
"We are looking forward to working with him and we are confident that he will bolster what is already a strong squad of players.
"Like Marcos, he will take a period of time to bed in because he will be playing in a different country, but we are very confident that he will have a successful time here."
Source: PA
Source: PA