Arsenal defender Laurent Koscielny was surprised by Arsene Wenger's touchline bust-up with Chelsea boss Jose Mourinho on Sunday.
Koscielny believes Wenger lost his head on that occasion.
"It's a long history of friendship between the two coaches," Koscielny said.
"The facts are that after Cahill's tackle, I think the coach was a little upset because three days before Alexis Sánchez received the same tackle against Galatasaray. The player only got a yellow card.
"It's true, he [Wenger] flew out of control."
