The Spanish defensive utility is expected to leave Bayern this summer, with just over a year to run on his current deal.
A move to Athletic has been mentioned, where president Aitor Elizegi confirmed last month: “He can still help Athletic. It is important that he wants to come and do the best he can. And that he gives us something that is currently missing.
"He shouldn't block the perspective for an aspiring youngster either."
Martinez spent six years previously with Athletic between 2006 and 2012.