Piazon has made just three appearances for Chelsea since joining from Sao Paulo in January last year and made his Premier League debut as a substitute in the 8-0 hammering of Aston Villa before Christmas.
The Brazilian has now been allowed out on loan to gain further first-team experience at Malaga, who will face Porto in the last 16 of the UEFA Champions League next month.
"We have an agreement with Malaga for Lucas Piazon to go on loan there until the end of the season," said Chelsea's interim manager.
Benitez has ruled out recalling Romelu Lukaku from his successful loan spell at West Brom, where he has scored nine goals in 22 matches since August.
The 19-year-old has expressed a desire to stay at West Brom beyond this season and Benitez feels Lukaku is benefiting from the experience.
"Romelu went there as a young player and he's doing well. He's getting experience in the Premier League," he said.
"You never say never because you might have a problem, but at the moment the idea is that he stays there and gains more experience."