Debuchy was dismissed midway through the second half for a two-footed challenge on Claudio Yacob as Newcastle slipped to their second straight defeat, sealed by Saido Berahino's penalty three minutes from time after goalkeeper Tim Krul had brought down Matej Vydra.
And while Pardew insisted there was nothing malicious about Debuchy's tackle on the West Brom midfielder, he accepted Lee Mason's decision to dismiss the France defender.
"I don't think we can have too many complaints," Pardew said.
"I think Mathieu has been our best player this last period, and he is an honest player. He genuinely went for the ball.
"There was no malicious intent, but you can't take off with two feet like that.
"We are going to suffer, and so will he. He will be a big miss for three games, and obviously it affected us today."
Pardew also admitted that Newcastle were fortunate not to have seen Krul sent off for his ill-advised lunge on West Brom substitute Vydra.
"I thought it was a penalty," he added. "Fortunately the forward had a big touch, otherwise we might have lost another player.
"That was the deciding factor in a very tight game.
"I can't fault the players. I thought they were terrific in their application and attitude but with this programme, with 10 men, you're always going to be struggling.
"I thought it was a game we had good control over but unfortunately we couldn't get the breakthrough before the sending off. Obviously that changed the game."
