McClean took a knock to his knee and was substituted in the 48th minute of West Brom's 2-1 loss to third-tier Bristol Rovers at Memorial Stadium on Saturday.
The Irishman was a last minute replacement for Matt Phillips, who was withdrawn from the starting XI because of a tight hamstring.
Tony Pulis told the club's official website, 'James' (injury) is the most concerning at the moment because it is in the knee area and we'll get that scanned to see what that tells us. Matty reported a tight hamstring so it made no sense to risk him.'
Chris Brunt also picked up a calf probelm in the same match and was substituted just before half time. Pulis added, 'we're hoping Chris' problem is not so serious. It's a question of whether he's strained his calf or it's just a result of landing awkwardly,'
Albion struggled to create any chances at Rovers but Pulis is more worried about the injuries than the performance. He said, 'the game is a pre-season game. There were some good things and some not so good things.'
'We are not playing for points, we are playing to get them fit for when the season starts. That's the most important thing. The disappointing thing for me is the two injuries.'