"The penalty hurt us, we have seen that they equalised with an invisible penalty", Valverde told reporters. "I think the referees in the Premier League are the best in Europe".
"But we knew that it was a hard ground to come to, even though they're in the bottom three".
Mateu had already angered Barcelona in the final minute of the first half, deciding against punishing Las Palmas goalkeeper Leandro Chichizola after he handled outside his penalty area when attempting to make a sliding clearance.
To help fund the move, Barcelona are tipped to offload midfielder Denis Suarez and the Daily Express also believes that striker Paco Alcacer could be moved on to free up space in the dressing room.
"I don't want to analyse the referee", added Valverde.
Whether the points gap stands at seven, five or four ahead of that clash, Atletico are a real threat.
Barca's lead at the top of LaLiga is now at five points and will be cut to two if they lose against Atleti at Camp Nou on Sunday.
"It would be an important match no matter what, with the first-place team playing against the second-place team", Barcelona coach Ernesto Valverde said.
Turkey worldwide Enes Unal scored the only goal at El Madrigal after just three minutes and Asenjo preserved the lead by saving a first-half spot-kick from Angel Rodriguez.
"I said some things that I shouldn't have (about a possible transfer to Manchester United) and I regret to have asked the fans to shut up a few weeks ago regarding something I did they didn't like". It did us a lot of damage - for how it was given and the sensation it left us with.
"This point gives us the impetus to keep fighting". These were moments in the match when I thought we had to keep hold of the ball.