Updated

NEW YORK (Reuters) - New England Patriots rookie linebacker Brandon Spikes has been suspended for four games without pay for violating the NFL's policy on performance-enhancing substances, the league said on Friday.

The suspension for the unnamed substance was effective immediately, starting with Sunday's game against the Chicago Bears, the NFL said in a statement.

Spikes will be eligible to return to the Patriots on Monday, January 3 following the team's final regular season game against the Miami Dolphins.

He would be eligible to participate in all playoff games, should the Patriots qualify for the postseason. New England have the AFC's best record at 10-2.

"The substance was a medication that I should have gotten clarification on before taking. It was not a performance enhancer or an illegal drug," Spikes said in a statement on the team's website (www.patriots.com).

"The integrity of the game is very important to me. I understand the league's ruling and apologize to my team mates, the fans and the Patriots organization for this mistake."

Spikes, a second-round draft pick by the Patriots from the University of Florida, has 61 tackles and one interception this season.

(Writing by Larry Fine; Editing by Greg Stutchbury)