The veteran attacker has raised the prospect in recent weeks.
But Mackay told Absolute Radio: "I understand where he's coming from. He's had over 20 knee operations. We make sure that we temper his training. He played more games last year then he has in five years. So, we temper his training so that he gets out there on the pitch in games.
"He's still got a love for Wales, the country so, he's not pulled out two or three years ago and decided to chuck international football. So, he's kept going with that. So, there is a point in his life where he'll decide that enough's enough. But, I've just said to him: 'See how you're feeling at the end of the season', because he might take a month off and think: "I'm really missing it I'm still in good enough shape to be part of it'.
"So, we're quite relaxed."
Mackay was speaking on Absolute Radio's Rock n' Roll Football Show with Ian Wright. Saturday's from 5pm.
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