I think it depends, it might be possible. The genjutsu has to be very strong for an Uchiha to fall prey to it and it shouldn't be something like the Tsukiyomi which tortures the victim for mere seconds but the victim feels as if it's been an eternity, because a few seconds won't be enough for the MS transformation to occur imo. It should be a strong real time genjutsu in which the speed of time in the genjutsu and real world do not differ and the victim goes through the same pain and suffering as is required for the transformation to occur.
never thought about it before. Good question.