Video footage showed the former AC Milan boss shoving Castro in the tunnel and PSG could even face a points deduction if the Professional Football League (LFP) decides to take action over the incident.
Even though Leonardo has claimed he was pushed into the official by accident, Fernandez has little doubt that he was fully aware of his own actions and should have known better.
"What bothers me most about Leonardo's action is that you know that you cannot touch a referee like that," Fernandez told RMC. "I once grabbed a referee by the hand when I left the pitch and got six months for it.
"The images speak for themselves here. Leonardo is obviously under a lot of pressure. There's undoubtedly something that led to this reaction. But he's sporting director at PSG, a big club with an ambitious project. You should know how to lose as well. It can happen."
PSG remains first in Ligue 1 following the weekend's draw and holds a seven-point lead over second-placed Olympique de Marseille.