In a statement issued by the team Saturday, the 26-year-old said he will enter a rehab facility.
"After careful consideration of recent events within my life, I have made the decision to enter a rehabilitation facility," Dareus said. "I feel this is the best decision for me, my family and my teammates as I move forward with my career. I appreciate the support of my teammates and the Bills organization through this process."
NFL Media Insider Ian Rapoport reported Tuesday that the suspension stems from "either failed or missed drug tests involving his use of marijuana."
"As a football team, as a family, we came together and we support Marcell Dareus 100 percent," Ryan said. "I'm excited about the young man trying to change his life."
Last year, the Bills gave Dareus a seven-year, $103.2 million deal with $60 million guaranteed to be a building block along the defensive line.
After a disappointing 2015 season, the Bills hoped Dareus could bounce back in his second season under Rex Ryan.
First, the young defensive lineman has to get his life in order. Hopefully rehab will help in that endeavor.