TAMPA, Fla. (AP) -- The Tampa Bay Buccaneers braced for life without Brian Griese on Tuesday, acquiring Tim Rattay from the ***** to back up young quarterbacks Chris Simms and Luke McCown.

Griese injured his left knee during Sunday's 27-13 victory over Miami, however the Bucs still haven't commented publicly on his condition or said how long he will be sidelined after helping them to a 5-1 start.

"We're getting some more analysis," general manager Bruce Allen said. "He's still on the team. He is wanting to play. We're hopeful that he can. But we're going to get the proper medical opinion."

Allen declined to discuss specifics of the injury, which occurred when Dolphins linebacker Zach Thomas rolled into Griese's leg, or what doctors have told the team about the quarterback's status.

What's clear, though, is Griese will be out for a lengthy time.

Simms replaced him against the Dolphins and will have two weeks to prepare for his first start of the season because Tampa Bay has a bye this Sunday.

The Bucs sent what was believed to be a sixth-round draft choice to the ***** for Rattay, a six-year veteran who lost the starting job in San Francisco after four weeks to No. 1 overall draft pick Alex Smith.

Allen said the Bucs explored the prospect of acquiring Rattay during the offseason and were excited to find he was available before the NFL trading deadline of 4 p.m. Tuesday.

To make room on the active roster, the team released rookie fullback Rick Razzano.

"We feel he'll be a great fit for our team," Allen said. "He'll come in and be our No. 3 quarterback. It gives us some great insurance and a feeling that we can sleep at night that we have a bona fide NFL starter."

Simms and McCown, like Rattay a former standout at Louisiana Tech, have made a combined six starts as pros -- all last season when Simms made two for the Bucs and McCown started four as a rookie in Cleveland.

Rattay, a seventh-round pick in 2000, started nine games last season and beat out Smith in training camp this year. But he performed poorly after an opening victory over St. Louis and was benched by coach Mike Nolan.

Rattay has played in 32 games with 16 starts. He has completed 356 of 586 passes (60.8 percent) for 3,941 yards, 24 touchdowns and 18 interceptions. He has a career passer rating of 81.6.

"He was the best quarterback we thought could help us right now," Allen said. "And the fact that he has experience allowed us to look at enough tape ... we feel very comfortable we know what we're getting."

At Louisiana Tech, Rattay started 33 games, finishing second in NCAA history with 12,746 yards passing. He was the third player in NCAA history with more than 100 career touchdown passes.