Keenan Allen's return from a season-ending kidney injury last year took a dreadful turn in San Diego's 33-27 overtime loss to the Kansas City Chiefs on Sunday.

Based on initial tests, Allen suffered a suspected torn ACL during the second quarter of the game, NFL Network Insider Ian Rapoport reported. Allen was down on the field in pain before being carted off the field. The team confirmed that he suffered a right knee injury.

It's a huge blow to the Chargers offense and QB Philip Rivers takes a bit of a hit to his fantasy value. The Chargers may have to turn to the run a little more going forward, especially with Melvin Gordon looking good in Week 1. But Tyrell Williams finished with 2 catches for 71 yards and drew a lot of positive press this summer. He's a name to watch for as a guy to get more snaps and targets, likely on the outside with Dontrelle Inman remaining in the slot. Travis Benjamin moves to the WR1 spot.

Chargers wide receiver Keenan Allen has been carted off the field late in the second quarter of their game against the Chiefs with what appears to be a serious right knee injury.

Allen was making a cut toward the sideline on a passing route when he went down. He ripped off his helmet as trainers began tending to him, and was helped into the back of a cart and taken off the field.

There was no immediate word on the extent of the injury. Allen, who missed the last eight games a year ago with a lacerated kidney, had six catches for 63 yards before he was hurt. If serious, it would obviously be huge blow to the Chargers offense as well as QB Philip Rivers. We'll continue to follow.

San Diego Fanfest spectators wondered why speedy newcomer Travis Benjamin sat out all drills, and why Keenan Allen, the No. 1 receiver, sat on the bench with a shoe off as trainer James Collins checked on both players.

HC Mike McCoy said Allen was limited to solo drills, due to having his foot stepped on Friday. “He’s fine,” the coach said.

McCoy didn’t specify Benjamin’s situation but said generally that he’ll rest players on certain days.

So once again, it was Tyrell Williams getting to take advantage. Williams had a 28-yard catch which QB Philip Rivers described as the top highlight for the first team offense. Williams is having a good camp and could be in line for more playing time with Stevie Johnson's injury. The story said Williams is of the Michael Floyd mold.

Tyrell Williams, a second-year pro, has seen extra work with the first-team offense in Stevie Johnson's absence.

Williams also worked heavily with the ones when a hamstring injury limited Travis Benjamin this spring. Benjamin seems back to full strength this training camp, running at full speed opposite Keenan Allen.

This falls right in line with news items we had yesterday right after Johnson went down. Williams is a bit of an unknown but has been taking advantage of injuries as far back as spring. The story also mentioned Dontrelle Inman as seeing plenty of wide-receiver reps in the early going of camp.

Keenan Allen got open fast and snatched passes, seven months after a lacerated kidney ended his season. If health allows, the 24-year-old looks on the verge of commanding a huge contract.

"Keenan Allen is bigger than I thought," said Chargers newcomer Dwight Lowery, a safety in his ninth season.

Allen racked up 67 catches for 725 yards and four touchdowns in eight games, so he was on pace for a 134-1550-8 season prior to lacerating his kidney. At the halfway mark, he was the #7 receiver in standard formats and #4 in PPR. He garnered 11.1 targets per game, but that number could decline a bit since Antonio Gates sat out four of those games. However, Allen saw 30 targets in three games with Gates, and in the third game (five targets), he only played 60% of the snaps due to the injured kidney. Given his usage, the fourth-year receiver a threat to finish as a WR1 in 2016.

The day has arrived when Keenan Allen rejoins teammates for the start of the Chargers’ voluntary workout program. Phase one of a nine-week regimen features two weeks of strength and conditioning. Allen will be a full participant Monday, the injury that ended a banner season mid-breath well behind him.

He lacerated his kidney Nov. 1 on that touchdown in Baltimore.

The ailment ended his season but not before eight games from which he can build.

“Just try to dominate,” Allen said, “knowing that I can dominate the league like I did last year for those eight games. Hopefully, I can come back and do that for a full 16. … I feel 100 percent. I have no aches, no pains. The kidney healed up really well. I’ve just been working. Ready.”

Allen racked up 67 catches for 725 yards and four touchdowns in eight games, so he was on pace for a 134-1550-8 season prior to lacerating his kidney. At the halfway mark, he was the #7 receiver in standard formats and #4 in PPR. He garnered 11.1 targets per game, but that number could decline a bit since Antonio Gates sat out four of those games. However, Allen saw 30 targets in three games with Gates, and in the third game (five targets), he only played 60% of the snaps due to the injured kidney. Given his usage, the fourth-year receiver a threat to finish as a WR1 in 2016.