Matteo Politano had put the minnows ahead at San Siro, but Nikola Kalinic blasted an equaliser in off the underside of the bar.
“I don't think it was an issue of one or two strikers, because we created a great deal in the first half and overall had over 20 shots on goal. What we lacked was vehemence and determination," Gattuso told Mediaset Premium.
“At the end of the day, we were even lucky to get a point, as we had gone behind. You can give all sorts of reasons for fatigue, but the fact remains we were sluggish in the final third."
He added: “We had over 20 shots on goal, sometimes the ball goes in and sometimes it doesn't. We had chances, we had lots of 50-50 issues, but it can happen after four or five months that someone's legs feel heavy.
“The important thing is not to seek alibis, because we'll go nowhere with them. I think we missed a big opportunity here to stay within reach of Champions League qualification."