Juve have confirmed they want to sign Aguero this week.
But Ferri says: "There are many problems at Juve, several players who they want to get rid of are unattractive to buyers. It is not easy to do and we must allow time for Juve to become competitive.
"If they are thinking that just by buying Aguero all their problems will be resolved - it would be a huge mistake.
"The fact that Juve is not in Europe may also affect their chances of signing the right players."