New England Patriots running back Brandon Bolden has been suspended by the NFL for four games without pay for violating its policy on performance-enhancing substances.

The league's announcement Friday did not specify the substance. The Patriots had no immediate reaction.

Bolden, signed as a rookie free agent from Mississippi, can return to the active roster on Dec. 3, one day after the Patriots game against the Dolphins in Miami. He was inactive for the past two games with a knee injury after rushing for 234 yards and two touchdowns in six games.

He ran for 137 yards on 16 carries and one touchdown in a 52-28 win over the Buffalo Bills on Sept. 30.

The Patriots are home against the Bills on Sunday.