The winger, a ??1.5m summer signing from Wigan, turned away from the Cross of St George and bowed his head during the pre-match ceremony before Albion???s 2-1 pre-season win against Charleston Battery in South Carolina.
Sky sources have been told Pulis is understanding of the situation, but has warned McClean to tone down his political stance in public.
McClean scored in the 2-1 win in South Carolina, a game in which Brown Ideye headed an 89th-minute winner.