"He needs to focus on getting himself ready," Marrone said according to NFL Media's Albert Breer.
It's unclear when Dareus will be in shape enough to practice. And it's unclear if the NFL will allow Dareus to suit up early in the season.
Dareus was arrested in April in Alabama and charged with possession of synthetic marijuana and drug paraphernalia. A month later, he was charged in connection with an alleged street-racing accident. Dareus was also benched by Marrone late last season for repeatedly missing team meetings.
The Bills hold the first practice of training camp on Sunday evening, but they will be without two of their young, promising defensive Pro Bowlers. Linebacker Kiko Alonso was lost for the year with a torn ACL. Dareus will be back on the field for the Bills eventually; Marrone knows that some players are worth being patient for.