In-demand Angel Di Maria is Real Madrid's best player, according to Atletico coach Diego Simeone.
The Argentinian winger, who is a reported target of Manchester United, came on as a substitute in the 75th minute in Tuesday's 1-1 draw against city rivals Atletico in the Spanish Super Cup first leg.
Real took the lead five minutes later through James Rodriguez before Raul Garcia equalised for Atletico with two minutes remaining.
"In the second half Real Madrid played better when Di Maria entered the pitch," Simeone told Spanish newspaper Marca.
"It's logical because he is the best player they have.
"I truly believe that Di Maria is the most destabilising player they have and that makes Madrid play well.
"He complicated our lives a little bit defensively."
Real boss Carlo Ancelotti admitted prior to Tuesday's game at the Santiago Bernabeu that he was not sure whether Di Maria would remain at the club.
Media reports claim United are ready to spend £100million, a £50m transfer fee and around £200,000-a-week wages on a five-year deal to lure the Argentina international to Old Trafford this month.
"I don't know what Di Maria has decided," Ancelotti said. "But I know that he's training and that he will help us.
"Until August 31 it will continue the same way and after that everything will be cleared up and things will return to normal."