However, Petkovic warned that the Bundesliga outfit are more dangerous away from home and stressed the importance of maintaining winning ways against Fiorentina on Sunday evening.
"Our chances of qualifying are now 51%," Football Italia quotes the 49-year-old as saying.
"We have to be wary of Stuttgart, as they tend to play better on their travels than at home, but if we play like this then I think we can have some satisfying moments in Europe as well as Serie A.
"Now we have to think about Fiorentina, as a victory will be necessary for morale."
The quarter-final draw will take place in Nyon, Switzerland on March 15.