Barcelona president Josep Maria Bartomeu says he'll write a letter of complaint to Luis Rubiales, the president of the Spanish Football Federation (RFEF), after they were denied a penalty during their draw with Real Sociedad.

Gerard Pique appealed for a spot-kick after he went down under the challenge of Diego Llorente in the area.

Referee Gil Manzano gave nothing, which further infuriated Barcelona after Sergio Busquets gave away a penalty for tugging on Llorente in the first half.

VAR wasn't used for the incident involving Pique and Bartomeu now wants to know why.

"I think it was a penalty," Barcelona's head of Institutional Relations Guillermo Amor said of the Pique incident.

"Everyone could see it was [a penalty]."