DeMerit is expected to take part in the FIFA World Cup this year with USA who in their drawn group faces England, Slovenia and Algeria.
jay demerit
However he is expected to travel to South Africa without a club were no doubt other Championship sides will be keen to sign the defender.
"Jay is out of contract and financially we are not in a position to offer him a new contract and he has the World Cup (with USA)," Mackay told the Watford Observer.
"Jay also has an awful lot of other things in his life outside football that he is going to think about and even what country he is going to be in next year.
"I don't even think Jay knows what is going to happen after the World Cup yet but he goes with my best wishes."