The 32-year-old made the switch to Merseyside on a temporary basis on deadline day after slipping down the rankings at Manchester City.
"He is playing with the desire and enthusiasm of an 18-year-old and has been a great player for us and I just want him to keep enjoying his football at Everton for as long as we can, but it is not the right time to be talking about joining us permanently," the Manchester Evening News quotes Martinez as saying.
"I wouldn't put that in his mindset at the moment, all I want him to focus on is to keep enjoying his football and develop that competition behind the scenes. That is the only thing that matters at the moment."
The Toffees are preparing for their Premier League clash against Aston Villa tomorrow.