Coach Chan Gailey announced Thursday that Merriman will not play against Detroit (2-6) this weekend, and is out indefinitely after aggravating an injury to his right Achilles tendon in his first practice a day earlier.
The injury occurred early into Merriman's first practice with the winless Bills (0-8), a week after he was claimed off waivers from San Diego. The injury is also to the same tendon that's been bothering him for much of the past year.
"It's short-term more than long-term, but we'll just wait and see," Gailey said. "We'll see what happens next week, or it might be the next, I don't know. We're going to get him well. That's the most important thing. Let's get him well before we put him on the field."
Merriman was hurt early into practice during an individual non-contact drill. After dropping back, Merriman pivoted to his left when he pulled up and began hopping in pain. After consulting with trainers, the player limped off the field and escorted into the team's training facility.
Though he missed practice on Thursday, Merriman was at the facility receiving treatment but did not make himself available to reporters.
The injury is the latest setback for a once-feared pass rusher who earned the nickname "Lights Out" for his hard-hitting style in San Diego.
After registering 39½ sacks in his first three NFL seasons, Merriman's managed just four in his past three years. He missed most of the 2008 season after undergoing reconstructive knee surgery.
His career in San Diego effectively ended last month when the Chargers placed him on injured reserve because of a left calf injury. Merriman had also complained about an injury to his Achilles tendon.
Merriman did pass a physical upon reporting to the Bills last weekend. And he was in street clothes on the Bills sideline, watching Buffalo's 22-19 loss to Chicago at Toronto on Sunday.
On Monday, Merriman said he's been working out the past few weeks, but didn't know if he was in "football shape" yet. He was eager to begin playing.
"Whatever they want me to do, I'm there," Merriman said. "We're all on the same page in getting ready to go play football."
The Bills were counting on Merriman's pass-rush ability to spark a defense that's had difficulty pressuring opposing quarterbacks. The lack of pressure is being blamed on Buffalo managing a league-worst one interception this season, a year after finishing second with 28.
"It's not good," linebacker Paul Posluszny said, when informed of Merriman's status following practice. "It's the opposite of good."
In claiming Merriman, the Bills picked up the remainder of the player's one-year $3.27 million contract.