Marotta also praised the Belgian-born youngster claiming he has big promise and is someone that would fit in well at Juventus.
United are in negotiations with the midfielder over extending his contract, with just eight months remaining on his current deal.
Current Juventus star Paul Pogba was in a similar position to Januzaj when he was at Old Trafford and the French youngster chose to move to Turin rather than stay in England.
Moratta claims that Januzaj could do the same and that United should have tied him down a lot earlier.
“If they fear another case like Pogba’s then they are right,” Juve’s general manager said.
“It’s difficult to understand how we can reach a stage eight months prior to the contract expiring without seeing a renewal.
“Januzaj is a player showing big promise. He is a player of great quality.”