A Chargers offense that has struggled to move the ball and score consistently was dealt a significant blow on Monday when Philip Rivers was placed in concussion protocol, an injury that could snap the veteran quarterback's streak of starting 194 consecutive regular-season and playoff games since 2006.
Rivers, 35, has not been ruled out for Sunday's game against the Buffalo Bills in StubHub Center, but his status is in question. He will undergo numerous tests throughout the week, and the team can wait until as late as Sunday to determine whether he can play.
"It was news to me this morning," Chargers coach Anthony Lynn said Monday. "Phil came in today and self-reported concussion symptoms. He's seen our doctors, and we'll evaluate him for the rest of the week. … His chances of playing, I hope, are good."
If Rivers can't go, Lynn said backup Kellen Clemens, a 12-year veteran who has completed six of 10 passes for 73 yards and a touchdown over the past 3 ½ seasons for the Chargers, would start.
"We've got all the confidence in the world in Kellen," veteran tight end Antonio Gates said. "When you've put in the work and made the sacrifices he has, we feel no different about him than we do any other backup quarterback on our team.
"Philip is obviously the cornerstone of what we do and how we implement our game plan, but I'm quite sure that we'll do things that would maximize Kellen's ability if need be."
Rivers, who has completed 194 of 323 passes for 2,263 yards and 15 touchdowns this season, has been one of the most durable players in NFL history. Only three other quarterbacks — Brett Favre (321), Peyton Manning (227) and Eli Manning (220) — have longer streaks of consecutive starts.
Rivers has played through several injuries — a torn knee ligament in the 2007 AFC championship game at New England, a bulging disk in his lower back and a rib-cage sprain in 2014 — but this is believed to be his first diagnosed concussion.
Lynn said he saw "nothing at all" after Sunday's 20-17 overtime loss to the Jacksonville Jaguars at EverBank Field that would indicate Rivers sustained a head injury, but there were two plays on which Rivers absorbed, and delivered, jarring hits.
The first was late in the first quarter, when Rivers, after releasing a pass, was hit high by Jaguars end Yannick Ngakoue and low by lineman Dawuane Smoot, who was blocked into the back of Rivers' knees. Rivers was upended and fell flat on his back, snapping his neck and head on the turf.
The second was in overtime, after Rivers' long pass intended for Travis Benjamin was intercepted by Jaguars cornerback A.J. Bouye near midfield. Bouye returned the ball 51 yards before Rivers knocked the defender out of bounds at the two-yard line with a helmet-to-helmet hit.
"It was a multitude of hits," Gates said. "If you watch, he hit the ground a lot, and there was that one situation where one guy went high and one guy went low. If I was a betting man, that would have probably been the hit that put him in the situation he's in now."
Gates and Rivers have connected on 85 touchdown passes, the most of any quarterback-tight end duo in NFL history. The last Chargers quarterback other than Rivers to throw Gates a scoring pass? Drew Brees in 2005.
"Man, I haven't even played a game without him other than the first couple of years I was here," said Gates, who joined the Chargers in 2003. "It would be a different feel, but at the same time, I think him being around, being able to communicate, his presence, will help us win this game."
Rivers' play hasn't led to many wins this season. The Chargers are 3-6, and Rivers has a career-low quarterback rating of 87.8, which ranks 19th in the NFL.
Clemens, 34, has 21 career starts but hasn't played regularly since 2013, when he started nine games for the St. Louis Rams, completing 142 of 242 passes for 1,673 yards, with eight touchdowns and seven interceptions. The Rams went 4-5 in those starts.
"I feel fine about Kellen," Lynn said. "He's well-prepared. He's a veteran … and he's been in this system long enough. He knows this offense like the back of his hand, so it won't change very much."
Lynn said right tackle Joe Barksdale, slowed all season by turf toe in his left foot, will miss his fourth straight game on Sunday. He will be replaced again by Michael Schofield. … Linebacker Hayes Pullard, inactive for Sunday's game in Jacksonville, will be limited in practice this week.