It may, but only by increasing it. Your child will also be able to use English to form friendships with children outwith the Gaelic-medium school or unit and can participate in out-of-school activities through the medium of English. (S)he will also, however, have access to another community through school and Gaelic-language activities like Fèisean and Sradagan.
The central location of GME and the distances that pupils often have to travel to access GME can create difficulties for parents transporting them to and from extra-curricular activities. Your local branch of Comunn nam Pàrant (Gaelic Parents' Association) will put you in touch with the local Gaelic support network.