Gary Neville was scathing of Jesus Gil Manzano, with the Valencia coach labelling the referee "a joke" after the club's four-match winning streak came to an end against Athletic Bilbao.
Neville felt Valencia were denied two penalties in Sunday's 3-0 loss at home to seventh-placed Athletic in La Liga.
Valencia's appeals for a penalty following a challenge on Andre Gomes from Xabier Etxeita were waved away by Gil Manzano in the first half, while shouts for handball fell on deaf ears after the break.
And speaking afterwards, Neville slammed the match official, telling reporters: "I thought the referee was a joke. It was embarrassing we didn't get two penalties.
"I've not blamed referees in any of our games, but I thought his management of the game was awful. Some of the things he did were incredible.
"We've been a very soft coaching staff towards referees, we've tried to be respectful because we know it's a difficult job, but I don't understand how we didn't have one of two penalties, one for Andre Gomes, the other for the handball.
"I don't have a clue. And he booked three of our players and I don't know how many fouls they had compared to us.
"There were three factors in the defeat: first the referee, secondly we missed chances, and third, we didn't react to conceding the first goal."
Valencia are 12th in the standings, seven points above the drop zone after 26 rounds.
And despite the defeat, Neville - whose Valencia will lock horns with Athletic in the last 16 of the Europa League - added: "I enjoyed watching us play, we were a team that looked confident, we looked like we were a team in control, and Bilbao had problems with us.
"I was amazed we didn't go 1-0 or 2-0 up, I was amazed we didn't get a penalty. It feels like a terrible day and it is, but it wasn't the story of the day for me.
"We leave here with a bad feeling, but I'd argue that was the best we played in the first 70 minutes. The problem is we haven't taken our chances."