The Giallorossi have been alternating losses with victories in recent weeks and they fell to a 4-1 defeat at Atalanta on Sunday.
"We're fluctuating," he told Radio Anch'io Lo Sport. "We go from balanced performances to those like in Bergamo.
"This is consigning us to mediocrity and we can't accept that. The young age of our players can not be an excuse for our negative performances either.
"Now we just have to pull ourselves together so that we are ready for the derby against Lazio and our other upcoming games."