The 20-year-old swapped the north west of England for Turin last summer, departing Old Trafford on a free transfer having grown disillusioned with life under then manager Sir Alex Ferguson.
Pogba has impressed in Italy, becoming a first-team regular with the Old Lady, and made his debut for France earlier this year.
Juventus are said to be close to agreeing fresh terms with Pogba, but president Agnelli admits if a huge bid came in they would not be able to keep hold of him.
"If I was to judge it from a footballers' point of view, Italy is no longer the final destination but a transit destination," he said of the fall in Serie A's standing at the Leaders in Football conference.
"I am trying to think what will be of us in two or three years' time if we get a massive offer for one of the best talents we have today, Pogba, the French 20-year-old.
"Would we be able to retain him? I don't know. I don't think at the moment we have the strength to retain such a player.
"Look at what happened to AC Milan. They had to give away Zlatan Ibrahimovic and Thiago Silva to pay the cheques.
"At the end of the day you can be attractive, but you also need to have the economic strength."