The Oakland Raiders have to do it without their head coach.

Dennis Allen left the team after Sunday’s 20-17 loss to Cleveland to be with his father, who has a serious medical issue. Allen is expected to rejoin the team on Wednesday night and be on the field Thursday when theRaiders (3-9) host the Broncos (9-3).

But until then, offensive coordinator Greg Knapp will oversee the team and defensive coordinator Jason Tarver will map out the defense.

“This is a pretty unique season, both on and off the field, I’ll say that,” Tarver said Monday. “There’s a bunch of adversity and the true character of a man and a coach and whoever is to, no matter what the circumstances, be a pro and handle your business. But I’ve been a part of a lot of different situations, both in this league and in coaching, but there’s some unique things that have happened this year.”

Allen is with his family in the Dallas area helping to care for his 66-year-old father, Grady, a former NFL linebacker with the Atlanta Falcons. Knapp said he texted Allen on Monday morning to pass on good wishes and planned to talk to the head coach as the team prepared for the Broncos.

Oakland did not practice on Monday and will have two brief practices before the game Thursday. With the short week, the position coaches had begun some of the scouting of the Broncos last week to allow the coordinators to put together the game plan on Sunday night and Monday.

Allen, a former defensive coordinator in Denver, is typically heavily involved in the defensive game plan, while giving more general tips about philosophy for Knapp to use on offense.

“Today we went right into a normal Tuesday routine for coaches,” Knapp said. “We started game planning this morning for Denver, and then our practice schedule for the next two days will obviously be a little bit shorter because our guys need to still recover from this game and get ready for the next game. From a game-plan standpoint, you condense maybe three days of practice into two. From a coaching standpoint, you’ve done a lot of work ahead of time, so you can make it happen a little bit sooner during the week.”

While Knapp is officially in charge of the team while Allen is away, he said the only real additional responsibility he will have is to decide when to blow the horn to move to the next practice period.

Some of the players just learned of Allen’s absence on Monday and wanted to pass their best wishes on to their coach and his family. They said it will be hard to concentrate entirely on the Broncos knowing what Allen is going through.

“I think it will because obviously we’ll be caring about his situation, just wondering what’s going on,” cornerback Michael Huff said. “But we know we have a game to get ready for. It will because we’ll be worried about him, but I think we’ll still walk on the field and focus.”

The Raiders will need to be at their best to have a chance against the Broncos. Oakland has lost five straight games and was carved up by rookie Brandon Weeden on Sunday in the loss to the Browns.

Now the defense must deal with Manning, who was 30 for 38 for 338 yards and three touchdowns in Denver’s 37-6 home win over Oakland in Week 4.

The Raiders are also dealing with a number of injuries in the secondary, with starting free safety Matt Giordano, backup safety Mike Mitchell and backup cornerback Phillip Adams all leaving Sunday’s game with concussions.

The three will need to pass the league’s concussion protocol in order to play Thursday, which could be difficult because of the short week.

That could lead to a patchwork secondary on Thursday night.

“You’re never really ready for Peyton Manning,” Tarver said. “It’s a matter of getting on the same page and having enough coverage looks to hopefully slow down his progression and challenge guys in coverage, that’s what we need to do.”

NOTES: RBs Darren McFadden and Mike Goodson are expected to play after missing the previous four games with sprained right ankles. … The Raiders are hosting their first Thursday game since Oct. 25, 1979, against San Diego. They have played eight Thursday road games since then.