Suddenly, everyone’s looking at the backup quarterback

Never mind that old notion about the backup quarterback being the most popular guy in town.

In the NFL, backup quarterbacks are suddenly the busiest guys in town.

A rash of injuries around the league has teams scrambling to get their reserve signal-callers ready for Week 6 games, with the Buffalo Bills going to the most extreme measures. They’ve promoted Thaddeus Lewis from the practice squad and plan to start him Sunday against Cincinnati.

“Thad gives us the best chance,” Bills Coach Doug Marrone said Monday in a statement posted on Twitter. “We’re going to give him an opportunity to see what he has.”

The Bills have temporarily lost rookie quarterback EJ Manuel to a knee injury, and that first-round draft pick isn’t expected to be ready for a few weeks. Undrafted rookie Jeff Tuel stepped in for the injured Manuel in Thursday’s game against Cleveland and was ineffective, completing eight of 20 passes for 80 yards with an interception.

Lewis is on his fourth team, having previously worn the uniforms of the St. Louis Rams, Cleveland Browns and Detroit Lions. He has appeared in one game in his career, getting the start for the Browns in last season’s finale against Pittsburgh. He did a respectable job, completing 22 of 32 passes for 204 yards with a touchdown and an interception in a losing effort.

The Bills are one of several teams groping for answers at the position. Philadelphia’s Michael Vick left Sunday’s game because of a hamstring injury and was replaced by Nick Foles, who finished the victory against the New York Giants.

Eagles Coach Chip Kelly said Monday he has yet to make a decision about which quarterback will start Sunday against Tampa Bay, although he reiterated that when Vick is healthy, the job belongs to him.

“I don’t know if he’ll play Sunday,” Kelly said. “Right now he’s day to day. We’ll see how he goes through the rehab process.”

But Kelly left open the possibility, maybe a remote one, that Foles could earn the job for good if he plays especially well.

“If he plays well? Yeah, there’s always open competition,” Kelly said. “So if Nick goes out there and throws 100 for 100 and throws 27 touchdown passes, then, yeah.”

Ryan Fitzpatrick, the onetime starter in Buffalo, is standing in for the injured Jake Locker in Tennessee and draws the difficult challenge of playing at Seattle on Sunday.

Locker, who played at the University of Washington, was no doubt looking forward to going back to compete in the Pacific Northwest but is expected to be out as long as two months because of a hip injury.

In Jacksonville, Chad Henne is warming up his arm for Sunday’s Jaguars game at Denver, as Blaine Gabbert is expected to miss the game because of a strained hamstring.

The winless Jaguars are 28-point underdogs against the Broncos, the largest spread in NFL history, and Sunday lost the No. 2 overall pick for the season, left tackle Luke Joeckel, to a broken ankle. Earlier in the week, Jacksonville traded another left tackle, Eugene Monroe, to Baltimore.

Two other high-profile quarterbacks have arrived and departed in the last couple of days.

Josh Freeman, the former first-round pick released by Tampa Bay, signed a one-year deal with Minnesota on Sunday but, Vikings Coach Leslie Frazier said, won’t be in the mix to start Sunday against Carolina.

“We think [Freeman will] be able to help us,” Frazier said Monday. “To what degree, only time will tell.”

Meanwhile, Oakland parted ways Monday with quarterback Matt Flynn, who a year ago lost the starting job in Seattle to then-rookie Russell Wilson.

Flynn was the Raiders starter at the beginning of training camp but ultimately lost the job to Terrelle Pryor, who played well in a Sunday night victory over San Diego and now prepares to play at unbeaten Kansas City.

Don’t feel too bad for Flynn, who backed up Raiders bust JaMarcus Russell at Louisiana State. Despite starting a total of one game during the last two seasons, Flynn has pocketed $14.51 million.

Thumb’s down

Green Bay’s Clay Matthews was hurt doing what he loves doing — sacking the quarterback.

The Packers Pro Bowl linebacker could miss several weeks or more because of a broken thumb, sustained when he was sacking Detroit’s Matthew Stafford on Sunday.

“I’m hopeful it’s not season-ending,” Packers Coach Mike McCarthy said Monday. “I think we’re all hopeful, but you have to get all the opinions and make sure you always do right by the player.”

sam.farmer@latimes.com