Genoa won 2-0 in Rome.
"We were unable to score and Genoa deserve compliments. They took the approach they had to take, which was to wait and pounce on counter-attacks," Petkovic told Sky Sport Italia.
"It above all hurts to drop these points, as we have already left a few too many along the way. Overall I remain optimistic and wait to get the full squad back as soon as possible.
"Once again we had few options today, so we have to keep picking up points everywhere we can. I haven't had the opportunity to play even three games in a row with the same players.
"If we had scored even one of those chances today, it would've been a different match. The lads gave their heart and soul today, but Genoa scored with the first shot on target.
"We made a few naive mistakes that were down to a lack of concentration. We were lacking that extra 10 per cent of determination to either prevent a goal or score one ourselves."
For breaking stories and all the great banter like us on Facebook: facebook.com/tribalfootball