Ronald Koeman has accused Liverpool boss Jurgen Klopp of making "disparaging" remarks regarding Barcelona's bitter rivals Real Madrid.
Klopp appeared to aim a dig at Madrid following the Reds' 3-1 Champions League quarter-final first-leg loss in the Spanish capital on Tuesday.
The match was played at Estadio Alfredo Di Stefano, the home of Los Blancos' reserve side, while renovation works continues at the iconic Santiago Bernabeu.
"This here tonight was really strange because it was a difficult situation in the stadium, but Anfield is at least a proper stadium and that will be good for us," Klopp said.
Zidane had little to say regarding Klopp's comments, but Koeman has now waded in ahead of Saturday's El Clasico clash at the same ground.
"Madrid are used to playing on that pitch and the opponents have to play there, and that's that," he told reporters. "For players the tough thing is playing without any fans.
"It's disparaging to a big club like Madrid [to say it is like a training pitch]. They've chosen the time to do renovation works at their stadium and they've chosen well."
Koeman previously managed Liverpool's local rivals Everton between June 2016 until October 2017.