An otherwise unknown head of Alexander the Great?

Among the huge amount of debris and parts of statues that have been unearthed in Pergamon, modern Bergama in Turkey, there is this colossal marble head. It probably was decorating the largest room of the upper terrace of the Gymnasium.

[Picture from the MET]

Best known in Pergamon is its unique altar dedicated to Zeus that has been entirely moved to the Altes Museum, Staatliche Museen in Berlin (see: Pergamon is simply huge). The altar is a statement in its own right and leaves little or no space for other details, whatever their size, condition or beauty.

One of such an odd artifact is the partial remainder of a head, probably designed to be the central figure of a circular medallion of approximately 1.2 meters in diameter. It seems to be one of kings that ruled over the Pergamon Empire since similar heads once decorated the walls of this Gymnasium. It is not impossible either that it represents Alexander the Great. Why not? Time-wise the marble fits the 2^nd century BC, but that is not certain either.