West Brom coach Tony Pulis conceded his team "weren't at it" in their 2-0 defeat at Crystal Palace on Saturday.
Pulis' side offered little as an attacking threat and were undone by a Yannick Bolasie header and a late Yohan Cabaye penalty as they slumped to a third defeat in all competitions.
"I don't know if it's confidence or what but we have to sort it out," he said.
"You can't go from a performance or eight [out of 10] and then drop to a three or a four. They certainly weren't at it today.
"Against Villa we played really well and then you get that performance. It's chalk and cheese, it's really disappointing."
Evans and McAuley will be of particular concern for Northern Ireland heading into an international break during which they could clinch a place at next summer's European Championship.
Pulis said: "It's a concern for Northern Ireland with the two games they've got. Whether they'll travel I don't know.
"We want to help the Home Nations as much as we can, fingers crossed they'll be okay. If they are near then we'll let them go. The doctor will scan them tomorrow and then we'll know whether they are serious or not."
