Real Madrid and Spain midfielder Isco lashed out at Spanish paper Diario AS following the publication's claims of him refusing to warm up during Saturday's Clasico after defender Nacho Fernandez was sent on.
The Primera Division's defending champions suffered a 3-0 loss at home to Barcelona, with Dani Carvajal getting sent off for a goal-line handball that resulted in a converted penalty from Lionel Messi.
Zidane had two substitutes - Marco Asensio and Gareth Bale - ready to go on prior to the sending off, but was forced to change plans to fill the void left by Carvajal and had Nacho go on instead.
Spanish radio station Cadena SER reported that Isco stopped warming up after that, and the story was further reported by AS.
Isco, though, rubbished the accusations via his Twitter account.
He tweeted: "Stop spreading sh*t, my other two team-mates [Asensio and Bale] were [still] going to go on... Since when can you make four substitutions?"
Madrid, meanwhile, look to be well out of the title race. Saturday's loss leaves them 14 points behind leaders Barcelona, and there is the possibility of them struggling to finish the season in the top four, with Sevilla trailing closely behind.
Zidane's men do have a game in hand on Barca, but it might count for absolutely nothing if results don't turn around quickly.