The Nerazzurri sit eighth in Serie A as their desperately disappointing form since the start of 2013 shows no sign of abating, meaning they could risk missing out on a Europa League spot next season.
The match could decide who qualifies for continental competition but, since the Biancocelesti are able to qualify if they win the Coppa Italia on May 26 or lose to Roma but the Giallorossi finish fifth or higher, Petkovic insists his side are under a lot less strain heading into the clash.
"For the Nerazzurri it will be a crucial match, because it is not only Lazio who are ahead of them. Winning in Milan for us, we can have an 80 to 90 per cent chance of playing in Europe next year," he told reporters on Tuesday.
"Most importantly, however, will be to enter the field calm and aware that we can improve our performance, as we did last week.
"It definitely will not be easy against [Andrea] Stramaccioni’s men, I expect they will be angry and have the desire to reverse the negative run of results they have had.
"But we do not have to worry about the opponent but only think of ourselves.
"I expect a response against Inter. The healing process for us is a long one, we need to continue to move forward and try to take these three points home.
"We will have to give everything and remain as compact as we were in the last game."
Stramaccioni’s job continues to hang in the balance and a defeat in their penultimate home game of the season could be fatal for his prospects of staying on in the summer and beyond.