The Raiders are gearing up for Sunday's matchup with the Titans in Tennessee.
On Wednesday, Jack Del Rio was asked: "What makes Delanie Walker such a dangerous guy?"
"That's a good question, and why is he not still across the Bay?" the Raiders' head coach responded. "The guy is a good player, man. And he's one of these guys that can be a mismatch in the secondary.
"He's big enough to cause problems for safeties, and he's fast enough to cause problems for linebackers. It's hard to put a corner on him all the time."
The 49ers drafted Walker in the sixth round of the 2006 draft.
Over seven seasons in San Francisco, the tight end caught 123 passes for 1465 yards and eight touchdowns.
In March 2013, he signed a four-year, $17.5 million deal with the Titans.
Over his first two seasons in Tennessee, he registered 123 catches for 1461 yards and 10 touchdowns.
He took his game to another level in 2015, racking up 94 receptions, 1088 yards and six touchdowns en route to the Pro Bowl.
Last week, he caught six passes for 83 yards and a score against the Lions.
"He's a good player. I have a lot of respect for his game," Del Rio said. "I think he's been a good player for a number of years now."