Arnette, who was already playing with a cast on his right hand with the thumb exposed after injuring it late in training camp, re-aggravated the injury in Sunday's loss at New England when he landed awkwardly on it after being hit by teammate Johnathan Abram on a sideline play.
"It's tough any time you lose a starter," coach Jon Gruden said. "I mean, we've lost five receivers, two right tackles and a left guard and a middle linebacker. So any time you lose a starter, it's a gut punch. But you've got to take punches in this league if you're going to survive, if you're going to be a coach."
Arnette, the No. 19 overall draft pick out of Ohio State and the third cornerback selected, has 13 tackles (10 solo) and one pass defended in three games for the Raiders, who are 2-1 and play host to the undefeated Buffalo Bills (3-0) at Allegiant Stadium on Sunday.
The Raiders secondary will be tested by Bills quarterback Josh Allen, who is the fourth player in NFL history with at least 1,000 passing yards (1,038), 10 passing TDs (10) and a passer rating of at least 120 (124.8) in his team's first three games of a season. Allen is also looking to join Steve Young and Peyton Manning as the only quarterbacks in NFL history with at least 300 passing yards and two passing TDs in each of his first four games.
With Arnette out, veteran Nevin Lawson figures to get the start at a cornerback spot, opposite Trayvon Mullen, with Isaiah Johnson and Keisean Nixon also in the mix to face Allen and receivers Stefon Diggs (20 catches for 288 yards and 2 TDs) and John Brown (10-152-2). Rookie Amik Robertson, who has been inactive the last two games, "can possibly get some snaps," Gruden said.
"So we've got a lot of young guys there that we're anxious to see and we're also confident in what they can do," Gruden said. "But they will be tested by this quarterback and the one next week. That's for sure."
Safety Dallin Leavitt was also activated from the practice squad Friday.
The Raiders travel to Kansas City to face Patrick Mahomes and the Chiefs on Oct. 11. Las Vegas will then have its bye week.
Arnette, who has yet to officially be placed on IR, is listed as out against the Bills this weekend, as are rookie receiver Bryan Edwards (ankle) and defensive tackle Daniel Ross (foot). Rookie WR Henry Ruggs III, who sat out last week's game at the Patriots with hamstring and knee issues, is doubtful after missing practice all week. Right tackle Trent Brown, who has not practiced since re-aggravating a calf injury in the opening series of the season at Carolina, is also doubtful. Same with receiver Rico Gafford (hamstring). Also, Abram (shoulder/thumb) and middle linebacker Nick Kwiatkoski (pec) are questionable, though both are expected to play.
"They've got a good quarterback, a good young quarterback," Lawson said of the Bills and Allen. "He's got a big arm. I mean, the dude can make any throw on the field. And they've surrounded him with a lot of weapons. They're very deep at the wide receiver position.
"[Allen] also knows how to improvise, so if the plays break down, he can extend the plays and make plays that's not scripted."
Lawson, who is in his seventh NFL season, has yet to record an interception in his career, 76 games with 59 starts.
"Hopefully when that opportunity comes," he said, "I can capitalize on it."