Armenulic's comments come days after American great Agassi announced his separation Djokovic to end his 11-month coaching relationship with former world No. 1.
"I was opposed to that co-operation since the first day because he didn't do anything for Novak. I think Novak helped him more because he made Agassi a coach. He left because he didn't know what to do," Armenulic told a webloid, Tennis World USA.
"Novak plays from the baseline better than Agassi and his return is better. Then how can Agassi help him? He never worked as a coach and had no experience how to help Novak," he continued.
Eight-time grand slam champion Agassi started his stint as Djokovic's coach in May last year.
However, Djokovic has been witnessing a downfall in his career after claiming his 16th grand slam at the French Open in 2016. The Serb also failed to defend his title at Roland Garros last year, before retiring injured in the Wimbledon quarter-finals.
Djokovic, 30, has been struggling to make a winning comeback since undergoing an elbow surgery following the Australian Open. He had suffered first-round defeats at both Indian Wells and the Miami Open last month.
After having more surgery on his elbow, he returned to court last month but fell to successive first-round defeats at Indian Wells and the Miami Open. (ANI)