Lazio were still in the hunt for the Scudetto at the turn of the year, but just two wins in their last 13 matches have left them struggling even to make it into Europe next season.
Back-to-back defeats against Juventus and Udinese have left the Biancocelesti two points behind fifth-place Inter Milan, but Petkovic is not giving up on a place in Europe yet.
"Apart from our more recent games, we've done well this season and now we've got to remain positive," he said.
"We need to take things game by game. In the end, everything will work out well.
"I am optimistic because the lads show me every day that they want to be successful. We just need get back into our optimal form as soon as possible."
Parma are also searching for their form after a recent slump which ended their slender hopes of challenging for a top-six finish.
Their forward Amauri is confident they can get back to winning ways in front of their own fans after losing their last game at the Stadio Tardini against Udinese.
"If we play with the spirit of wanting to give that little bit more, then we will get something out of it," he said at a press conference.
"We have shown it already many times, like against Torino. That is the spirit we need to have and we must never settle for what we have already got."