The Bosnian lamented a controversial decision to disallow the 31-year-old's goal against Palermo, in a result which sees Lazio drop off the pace in Serie A
Hernanes spared the Biancocelesti's blushes with a late equalising penalty, but there was earlier controversy when replays indicated Floccari had not been offside when scoring what would have been his second goal.
"The incident came down to a question of centimetres, and was really hard to judge," said Petkovic after the match. "These things do happen. Floccari showed me he deserves to play, however.
"Experimenting with three forwards tonight went badly, which was a pity really. In the end, a tie was a fair result, as Palermo did not deserve to lose either.
"We ought to be less timid on the road, otherwise we end up playing too deep like tonight."
The Olimpico outfit are in a surprise three-pronged race for the Serie A title alongside Juventus and Napoli, although this set-back ensures they lie five points behind.