Incognito, 37, initially went down with what the team described as an Achilles injury early in the Raiders' Week 2 victory over the New Orleans Saints.
"I hate to admit that, but we've tried everything we can," Gruden said. "Richie's tried everything he can to get back on the field. His season is over."
Incognito was coaxed out of retirement by the Raiders on a one-year "prove it" deal in the spring of 2019 and earned a two-year, $14 million extension, with $6.365 million guaranteed, as well as a Pro Bowl alternate nod despite missing four games. Denzelle Good replaced Incognito at left guard; he has played so well that Gruden called Good the team's "unsung hero" and quarterback Derek Carr referred to Good as the team's MVP.
Still, Incognito was part of the heavy financial investment the Raiders made in their offensive line. But due to injury and COVID-19 issues, the projected starting O-line of left tackle Kolton Miller, Incognito, center Rodney Hudson, right guard Gabe Jackson and right tackle Trent Brown played all of three snaps together this season, in the season opener.
In fact, Brown, who signed a record four-year, $66 million free-agent contract with $36.75 million guaranteed in 2019, has appeared in just two games this season -- three snaps in the season opener and at the Kansas City Chiefs on Oct. 11.
Brown, who injured his calf in training camp, suffered a mishap while being administered a pregame IV and has been on the reserve/COVID list twice, the most recent since Nov. 5. Gruden said Brown's return was "still up in the air" for the Raiders, who fell to 6-4 after Sunday night's heartbreaking 35-31 loss to the defending Super Bowl champion Kansas City Chiefs in the final minute.
"He's still, hopefully, about to get started here and resume his playing," Gruden said of Brown.
"It's a day-to-day operation and I'll know more from the trainer here on Tuesday morning."
"I don't even know who's in the lineup every week," Gruden said.
"I'm just waiting to see who's available for this Wednesday's practice and who, potentially, is available for Sunday's game. Like I said last night, I meant it -- I'm really proud of our players and our coaches. We've hung in there, we've fought and battled and scratched and we are what we are; we're 6-4 with six games left and we've got to get ready for the [Atlanta] Falcons."
Gruden also acknowledged that the second-quarter 15-yard unsportsmanlike penalty on the Las Vegas bench that moved the Raiders from the Chiefs' 1-yard line to the 16-yard line after a third-down incompletion was on him.
"I was outside the coaching box," he said. "Foolish penalty by me."
The Raiders kicked a field goal to take a short-lived 17-14 lead.
Also on Monday, the Raiders announced they signed defensive end Vic Beasley Jr. to the practice squad and claimed Takkarist McKinley via waivers from the San Francisco 49ers. The team also released defensive tackle Datone Jones from the practice squad; defensive end David Irving, offensive lineman Jaryd Jones-Smith, defensive end Chris Smith and linebacker Javin White were reverted to the practice squad.