Moukoko is yet to make his Bundesliga debut with BVB, but already has a worldwide reputation.
Eto'o told Goal: "There is a young player at Borussia Dortmund. His name is Youssoufa Moukoko. He is 15 years old and the next big player for me after Messi.
"As Lionel is getting older, we could prepare well for the future at Barcelona."
He added: "With Antoine (Griezmann) and Youssoufa on the front line, the team would be in a great position."