In early May, Dareus was arrested in his native Alabama and charged with possession of synthetic marijuana and drug paraphernalia. Four weeks later, he was allegedly racing teammate Jerry Hughes when he crashed his 2012 Jaguar into a tree near a busy intersection not far from Ralph Wilson Stadium.
Dareus was charged with reckless endangerment and ticketed for several traffic violations, including drag-racing.
The NFL could potentially discipline Dareus for his off-field troubles with a fine or suspension.
After the crash, Dareus consulted with Marrone and decided to take two weeks off from voluntary practices. He returned for the team's three-day mandatory minicamp in mid-June but did not speak to reporters.
He was last seen in Buffalo on July 1, when he made a brief appearance in court on his reckless driving charge.
Dareus has been a three-year starter in Buffalo since he was drafted with the third pick out of Alabama. He's coming off a career season in which he was credited with 71 tackles and 7 1/2 sacks and made his first Pro Bowl appearance as an injury replacement.
In other moves, the Bills also placed guard J.J. `Unga on the active/non-football injury list.
Starting cornerback Leodis McKelvin was cleared for practice. Coming off hip surgery, McKelvin was added to the roster after being activated from the active/physically unable to perform list.
The 6-foot-4 Gurley had one catch in three games with the Cleveland Browns last season. He has spent time with several teams since breaking into the NFL in 2011 as an undrafted free agent with Green Bay.
McIlwain has yet to play in an NFL game since breaking into the league in 2011. He was cut by Kansas City before the start of last season.
Both players participated on a tryout basis in Buffalo's mandatory minicamp last month.