Nuno Espirito Santo is not backing down.

The Wolves manager said on Wednesday he won't apologize for his blistering criticism of referee Lee Mason in the aftermath of his club's 2-1 defeat against Burnley at Turf Moor on Monday.

"I won't apologize for my words and thoughts," Espirito Santo said on Wednesday ahead of his club's visit from Tottenham Hotspur on the weekend.

After Monday's loss, the Portuguese manager railed against Mason.

"Football is a physical game, a game of contact and referees taking the decisions and being fair," Espirito Santo said. "But the referee is not good enough to whistle; Lee Mason is not good enough. It isn't about the major, crucial decisions. It is the way he handles the players - both teams lose their focus, they are always arguing the decision. He must improve because the game requires good refereeing and good handling of the game so the players are able to keep on performing."

On Tuesday, the FA announced it was opening an investigation into Espirito Santo's remarks.

Espirito Santo concedes that the timing of his words might not have been ideal, but that he never questioned Mason's ethics.

"They were not in the best moment to come across because it could be a bad interpretation," Espirito Santo said of his comments. "I never question the integrity of a referee. What I said was about the ability of the referee."

Wolves currently sits 11th in the table, 10 points behind leaders Liverpool and six adrift of Everton for the final Champions League place.