Goodson sat out of practice Wednesday with lingering soreness, one day after being hospitalized with a neck injury following a scary training camp hit.
Allen said he didn't know when Goodson will be back, but the coach doesn't anticipate it taking as long as a few weeks.
Goodson and Taiwan Jones were expected to compete for time as Darren McFadden's backup in Oakland. But with Jones also sidelined with a hamstring injury, former practice-squad member Lonyae Miller will have a chance to shine in Monday night's preseason opener against the Dallas Cowboys.
Goodson was taken away from practice Tuesday by ambulance with a possible neck injury after an on-field collision with teammate Philip Wheeler. Goodson lay prone on the turf for about 15 minutes. Paramedics and firefighters tended to Goodson, who appeared to move his legs and arms.
Goodson had movement in his extremities, and a CT scan and MRI both came back negative. Goodson returned to the team hotel Tuesday night, relieving his teammates and coaches.
"You never want to see somebody go down. That's a tough situation," said cornerback Ron Bartell, who missed most of last season with a neck injury. "I can definitely sympathize with what he was feeling at the time. I'm just glad to see that he's OK. It was a scare to all of us. It's a bad part of the game, you know, it's what we sign up for. You never want to see that happen. But we understand that it is always that possibility, it's what we do."
Goodson was attempting to catch a pass from Carson Palmer during a drill when he was leveled by Wheeler with a hit that could be heard at the opposite end of the field.
Allen said after watching the tape of the hit that he determined it wasn't a helmet-to-helmet infraction.
"It was a little bit of a freak deal," Allen said. "Mike kind of ducked a little bit. Philip kind of led with his shoulder a little bit and kind of lunged at him. It's things that happen in the game of football. It's an unfortunate occurrence. Fortunately, Mike is fine and we move on from it."
The Associated Press contributed to this report.