For Steph, this is one of the perks of being gainfully employed by the Celtics: “If it’s up to the team, he’ll have a positive effect,” the 75-year-old NBA legend told The Post yesterday at the NBA Store in midtown. “But you don’t know how much he’s been damaged psychologically playing here.” ‘Here’ of course, is with the Knicks, where his rocky tenure came to a disastrous end when it became clear that coach Mike D’Antoni had no intention of playing him and team president Donnie Walsh long refused to buy him out of his $21 million contract. When asked if he thought the point guard indeed had been ‘damaged psychologically’ by the Knicks, Russell said: ‘He may have been. No matter how strong you are, that kind of stuff that went on this season was so ridiculous.’”