The exact type of treatment Manziel is receiving is not known.
"Johnny knows there are areas in which he needs to improve in order to be a better family member, friend and teammate and he thought the offseason was the right time to take this step," Beckworth said. "On behalf of Johnny and his family, we're asking for privacy until he rejoins the team in Cleveland."
Manziel was fined an undisclosed amount by the Browns for arriving late to a treatment session in December. It is believed the tardiness was due to a party he threw the night before.
Browns general manager Ray Farmer released a statement supporting Manziel's decsion.
"We respect Johnny's initiative in this decision and will fully support him throughout this process," Farmer said. "Our players' health and well-being will always be of the utmost importance to the Cleveland Browns. We continually strive to create a supportive environment and provide the appropriate resources, with our foremost focus being on the individual and not just the football player. Johnny's privacy will be respected by us during this very important period and we hope that others will do the same."