"He's not quite ready to practice yet," Belichick said, adding that "When he's ready, he'll be out there."
The Patriots on Wednesday shipped a 2013 fifth-round draft pick to acquire Haynesworth, who appeared in only eight games for Washington last season, racking up a total of 13 tackles for the team that guaranteed him $41 million as part of a seven-year, $100 million contract in 2009.
Last season, he constantly feuded with new coach Mike Shanahan and was suspended for the final four games for conduct detrimental to the team. Now he's Belichick's issue.
Said Belichick: "There are things that we still need to do with Albert for him to be able to get on the practice field."
The Associated Press contributed to this report