Police Lt. Clinton Nichols said detectives are retracing Walker's activities in the hours before he was found injured Monday morning on a street off the Las Vegas Strip.
"That's one of the first things we do, backtrack what he did and where he stayed," Nichols said, adding that the investigation was still in the early stages. "We knew there was a large amount of cash taken, and some jewelry."
Nichols said he believed Walker would be released after a 24-hour stay at the hospital. A hospital spokesman said he had no immediate information about Walker's condition.
A Raiders spokesman said the team was in the process of gathering information and had no further comment.
On Monday, police Officer Bill Cassell said in a statement that Walker was taken to a hospital with "significant injuries" and was in fair condition at Sunrise Hospital and Medical Center.
Walker, 29, signed a six-year, $55 million deal with the Raiders after being released by the Denver Broncos in February.
Walker injured his right knee for the second time in his career last season and was limited to eight games and 26 catches in 2007.
Walker was a first-round draft pick by the Green Bay Packers in 2001 and had a breakout season in 2004 with 89 catches for 1,382 yards and 12 touchdowns.
He tore a ligament in his right knee the next season and played only one game.
He was traded to Denver in 2006 and bounced back with 69 catches for 1,084 yards and eight touchdowns.
