Heitinga has played just two Capital One Cup matches this season, with youngster John Stones preferred ahead of him as one of the substitutes in Saturday's 4-0 win over Stoke.
The Holland international has been heavily linked with a move to Fiorentina and Martinez said Everton will "try to help" the defender next month.
"Johnny has been an incredible professional since day one," said the Toffees boss. "He has been a big influence in the way we wanted to work.
"Johnny is a top footballer and we can understand if he doesn't play many minutes we will try to see if we can help him in January.
"But ideally I would like Johnny to start playing and have a big role on the pitch as much as he has off it.
"Sometimes the fans don't see that side. I really admire and value that.
"We all want Johnny to play and participate on the pitch but that is something we will have to assess over the next few weeks."