Both players have been linked with moves away from Roma this summer.
"De Rossi is calm," Juan said. "He's working with a great deal of enthusiasm and he has lots of quality.
"He is a leader and we want him to continue with us."
While it's understood that De Rossi wants to remain in the Italian capital, Juventus-target Vucinic has asked for a transfer.
"He's certainly working hard, but I can't really say any more about Vucinic than that," the South American noted. "I don't know what is going on in his head."