The 32 year old is on a season-long loan from Manchester City and is out of contract at the end of the campaign.
"I still think he is the best English player in his position," said Martinez.
"There will be other options, something I will always be aware of," added the Spaniard. "He is in a position where he can choose where his football happiness is going to be."
"The only thing he is focused on now is playing every game and playing as well as he can," added Martinez. "It is a joy to have him here."
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