Rookie Brady Poppinga's first NFL start served as an auspicious debut, but he will not receive a chance for a follow-up performance this year.

While covering a kickoff return in the fourth quarter, Poppinga tore the anterior cruciate ligament in his knee, and the Packers likely will place him on injured reserve.

"That's a significant injury," Head Coach Mike Sherman said. "And (it) will end his season."

Poppinga played well on Sunday, racking up four tackles. After missing three weeks in training camp with a hamstring injury, the former BYU defensive end had made strides at the linebacker position. Poppinga, a player with a non-stop motor, also led the team in special teams tackles.

"He was making progress," Sherman said. "He had been a force on our special teams unit."

Sherman ballparked Poppinga's return to football action at around eight months, but he could return sooner or later than that estimate.

"It depends on the individual," Sherman said.

Defensive coordinator Jim Bates spoke to Poppinga last night and said the 26-year-old remained upbeat despite the setback.

"His attitude is good," Bates said. "Brady will bounce back."

Such an injury never occurs at a good time, but Poppinga had steadily improved this season, and additional playing time during the remainder of the season would have helped him immensely. Although the rookie misread some plays on Sunday, Bates praised his energy level and hustle.

"He had some good plays," Bates said. "Of course, we knew that there would be some trying times -- first start and everything."

Following Poppinga's injury another rookie, Roy Manning, replaced him in the lineup. Na'il Diggs, who has been bothered by ailing knees all season, remains another option on the strongside to fill in for Poppinga. If Robert Thomas (quadriceps) returns to health, the Packers could move Paris Lenon from the weakside to the strongside. Sherman, however, did not reveal who will start at the outside linebacker positions against the Baltimore Ravens on Monday Night Football.

"We'll evaluate that," Sherman said. "We don't have to make that decision today. We have an extra day to work through those issues."

Poppinga had nine tackles on the year, including two sacks.