Petkovic will leave his role as coach of the Serie A side at the end of the season to take charge of Switzerland's national team - after they compete at the 2014 FIFA World Cup.
That has drawn the ire of Claudio Lotito, with reports suggesting that the club president could be ready to launch legal action as he apparently prepares to replace Petkovic with 68-year-old former Lazio boss Edy Reja.
Reja has been pictured leading the club's training sessions following the mid-season break, with Lazio set to resume their campaign on Monday with a home clash against Inter.
And Petkovic has been backed after claiming on Wednesday that, as far as he was concerned, he was still in charge at the Stadio Olimpico.
The organisation's president Renzo Ulivieri told Radio Radio: "Although you never know with Claudio Lotito, the procedure should see a coach receive written confirmation he has been fired.
"So far, Lazio haven't done that.
"This is why Petkovic, quite rightly, insists he still feels like the Lazio coach.
"He is practically fired anyway, as Reja is already training the team, so the only thing missing is the paperwork.
"Petkovic respected the rules of the rapport between Coach and club.
"As far as I can see, Petkovic is right. At the same time, Reja is confident of the situation. In order to register Reja, Lazio need to file the paperwork confirming Petkovic has been fired. That is where his certainty lies.
"Lazio have to complete this paperwork before Monday, otherwise Reja cannot sit on the bench against Inter."
