Helguson will not be allowed to play against parent clun Q.P.R. when the teams meet next month.
"He's a good addition and I'm delighted to have acquired him for the rest of the campaign," said Mackay.
"Right now I'm concentrating on what's happening between now and the end of the season. The focus was on getting Heidar, Henri Lansbury and Tom Cleverley in until the end of the season."