Forrest, along with Hoops team-mates Scott Brown and Adam Matthews, were asked by GB coach Stuart Pearce if they would be open to selection for his final squad. However, Neil Lennon's side are likely to be involved in European qualifiers in July when the Olympic football competition is under way.
Forrest said: "It has not been decided to be fair, it will be another couple of months. But I am still open to the idea."
He added: "It is obviously up to the club as well, it depends on whether they have fixtures in July.
"The club have said that if I want to play in it then they said I can but obviously if we have fixtures then obviously they won't let us go.
"There is still a long way to go until then."
Scottish Football Association chief executive Stewart Regan warned this week of a potential backlash against any Scotland players taking part in the Olympics, but Forrest side-stepped that threat by saying: "It is obviously a hard decision to make.
"We have the second half of the season to go with Celtic so we will wait and see how it turns out."