The Romans have failed to emerge triumphant in their last six league games and last weekend's 1-0 loss at Torino which followed their 4-2 defeat to Napoli piled further pressure on Petkovic.
"We are going through a difficult time and he (Petkovic) has to go after every game to explain what is going on," Hernanes said.
"One thing I know is that it's easy to be around and receive praise when things go well.
"But right now there are few people that could guide the team as he (Petkovic) is doing and has always done.
"I say well done to Vladimir Petkovic, a great coach and a great character.
"I am behind you."
Lazio are 12th in the standings and head into this weekend's match on the back of Thursday's goalless result against Trabzonspor.
The outcome allowed Lazio to progress to the last 32 of the Europa League as second in Group J.
"Right now our main problems is lack of goals," Petkovic said. "We are lacking self-confidence."
"We have to remain united in order to overcome this difficult time."
Rivals Livorno held AC Milan to a 2-2 draw last time out to halt a three-match losing streak.
"For us it is the first point against a big club," Livorno coach Davide Nicola said. "We showed great focus and will to win.
"We could have taken three points but I'm satisfied with the draw.
"Now we must give continuity to this performance."
The outcome moved Livorno to 18th place, one point behind safety.
Livorno have collected just four points of a possible 21 on the road this season but the visitors will be bolstered by the return of midfielder Leandro Greco, who has shaken off a back injury.
Lazio are without the services of injured midfielder Pereirinha until the new year.