The Blaugrana defender has admitted the harmony in the Roja dressing room was disrupted during a sequence of heated derby clashes between Spain's two biggest clubs
The Portuguese coach left Blancos after a controversy-ridden final year in charge and has in recent weeks been roundly criticised by Barcelona personnel for the venomous atmosphere he created in La Liga.
And speaking to Marca ahead of Spain's first Confederations Cup clash with Uruguay, Pique confessed that rivalry almost destroyed la Roja, with the Portuguese guilty of gouging then Blaugrana assistant Tito Vilanova's eye during one ugly incident.
"I trusted in the maturity of all of the players," the 26-year-old defender responded when asked if he feared tension in the Mourinho era might completely undermine the national team.
"But things got to the point where they crossed the line, and that made for a tense atmosphere. That's where everyone's maturity came in to play in order to say, 'That's enough.' It wasn't Mourinho who did it. It was some of the players who realised that it was getting out of hand."
Barcelona claimed the Liga crown in Mourinho's first season in charge at the Santiago Bernabeu and handed out a 5-0 beating to los Blancos at Camp Nou that same term and Pique feels the Catalans' dominance played a part in the ill-feeling between the sides.
"It got to the point where I think we were quite superior to Real Madrid and we were winning lots of trophies," the former Manchester United centre-half said.
"He tried to take the game off the field of play and I think he acted like that because he felt inferior to Barcelona, but at the end of the day the pitch is where things happen. Everything else just creates a bad vibe and generates things which aren't good for the national team or for this sport."