Those at Camp Nou moved to bring in a player of considerable promise after seeing funds made available by Neymar’s record-breaking switch to Paris Saint-Germain.
At 21 years of age, Dembele was supposed be a sound investment for the present and future, with his full potential set to be unlocked in Catalunya.
He is now a World Cup winner, having helped France to global glory in Russia, but he has failed to convince for Barca and is now seeing his future called into question during a troubled spell on and off the field.
“There are players who are worthy of playing for Barcelona and others who aren't and you can see that from the start,” former Blaugrana star Schuster told Onda Cero.
“You don't need three seasons.
“He [Dembele] had some great games for Dortmund at the start, but not that many. Barcelona is too big for him.”
The French forward is said to have angered Barca with his poor timekeeping and Schuster feels an error in judgement has been made by “not knowing what Dembele was like off the pitch”.
Those at Camp Nou are now being challenged to make a high-profile performer aware of his responsibilities, with a number of team-mates having already spoken out in support of their young colleague.
The German added: “I went directly to speak to the captains if a player was turning up one hour before the matches.
“If he hadn't changed it would have been my turn to speak to him.”
Dembele, who has managed six goals for Barcelona this season, will be hoping to play his way back into favour when the Liga leaders return to domestic action on Saturday against Atletico Madrid.