TAMPA, Fla. -- The Tampa Bay Buccaneers will have to finish their push for a playoff berth without rookie linebacker Kwon Alexander.

The fourth-round draft pick who has started all 12 games and been the team's most consistent playmaker on defense has been suspended for violating the NFL policy on performance-enhancing substances. He will sit out the final four games of the regular season without pay.

Tuesday's announcement by the league wasn't a surprise. Alexander was informed of the suspension last month, but said at the time he intended to appeal. He also said his positive test was linked to an energy drink he had used since high school.

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"I made a mistake by putting a product in my body that I did not know was banned by the league's policy," he said in a statement released by the team.

"It's very disappointing and frustrating that I won't be able to be with my teammates during this important final stretch of games, but I have to own up to my mistake, learn from this and ensure it doesn't happen again," Alexander added. "I have decided to drop my appeal in order to move past this issue and will focus on re-joining my teammates in four weeks."

The Bucs (6-6) have won four of their past six games to rebound from a slow start and climb into contention for a NFC wild-card berth.

Alexander won the starting middle linebacker job during training camp and has 93 tackles, three sacks, two interceptions and two forced fumbles.

Veterans Bruce Carter and Danny Lansanah have both played middle linebacker and likely will fill in for Alexander down the stretch.

"We are obviously disappointed to be losing Kwon at this point in the season. He made an error in judgment earlier this season and he has owned up to that situation," coach Lovie Smith said.

"We educate all players regarding the league's policies on performance enhancing supplements and, while we are disappointed in this situation, we will continue to stand by Kwon and support him as best we can until he is eligible to re-join the team following the last regular-season game."

The Bucs will face New Orleans, St. Louis, Chicago and Carolina in their next four games. The NFL said Alexander will be eligible to return to the active roster on Jan. 4, the day after team faces the Panthers.