Real Madrid captain Sergio Ramos has accused Lionel Messi of putting pressure on the referee in the tunnel at half time of Sunday's 2-2 draw with bitter rivals Barcelona.

Barca finished the first half with 10 men at Camp Nou as Sergi Roberto was shown a 45th-minute red card for lashing out at Marcelo, but the hosts held out for a point to keep their hopes of an unbeaten season alive.

Madrid were unhappy with a number of decisions which went against them in the second half - including what looked like a clear penalty when Jordi Alba tripped Marcelo - and Ramos has alleged that Messi may have influenced referee Alejandro Hernandez.

"Messi put pressure on the referee in the tunnel at half time," Ramos told reporters after the game.

"I don't know if there were cameras, and I don't know if he would have made other decisions in the second half.

"However, it's important to leave these things on the pitch, you have to show respect."

Barcelona are now only three games away from producing the first unbeaten season in the modern La Liga era.