Ernesto Valverde felt Barcelona were hurt by an "invisible penalty" after they let slip a first-half lead to draw 1-1 at lowly Las Palmas.
The LaLiga leaders appeared on course to restore their seven-point cushion over Atletico Madrid at the top of the table thanks to Lionel Messi's 21st-minute free-kick.
However, the hosts were gifted the chance to equalise straight after the break when referee Antonio Mateu pointed to the spot for an apparent infringement at a corner.
Las Palmas' Matias Aguirregaray tangled with Sergi Roberto as he headed against the post, with the rebound appearing to catch the retreating Lucas Digne on the arm.
"The penalty hurt us, we have seen that they equalised with an invisible penalty," Valverde told reporters.
"In the first half you could feel that the danger was there, more so with so many yellow cards. We went ahead in the first half, but the lead was slim.
"The penalty hurt us because of how it was, then they defended well and we tried to score. There was little consistency in our play too, and that cost us."
Valverde admitted he still had no idea why the official had awarded the penalty, with his own players also unsure over the reason behind the decision.
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.
"I don't want to analyse the refereeing," Barca's manager added in his post-match press conference.
"At half-time I spoke to him about the clear, deliberate handball outside the box by the goalkeeper.
"As for the penalty, I still don't know what he's given it for. In the dressing room it wasn't clear who had done what for the penalty."
While the draw maintains Barcelona's unbeaten record in the league this season, their lead is now down to five points ahead of Sunday's clash with nearest rivals Atletico at Camp Nou.