Bellamy revealed last week that he is unlikely to be fit enough to take on another qualifying campaign for his country and even suggested he could be in his last season as a professional.
The 34-year-old was absent from the Bluebirds squad that drew 1-1 with Hull on Saturday having played 90 minutes in World Cup qualifiers against Macedonia and Serbia.
Mackay is uncertain as to how long the forward will continue playing but accepts Bellamy's troublesome knees will force him to question how long he can go on.
"Craig is quite open in talking about it (retirement) so it's not a shock to anyone if it happens at the end of the season," said Mackay.
"He's someone at ease with seeing how the season goes and making that decision in the summer.
"I talk to him about Kevin Phillips and Ryan Giggs, who take it a season at a time, but there will be a point where, because of his knees, Craig wants a life with his family where he can walk about and not have arthritis in his knees for the rest of his life.
"And there'll be a point where he says 'that's not quite yet, I'm going to have another season'."
As for Bellamy's Wales career, Mackay is supportive but dubious.
He added: "There might be a point where he finally decides 'I've sweated and given blood for my country for a long time and I'll now come out of that to elongate my career'.
Source: PA
Source: PA