Remember the splash the Raiders made last year in free agency? A 333-pound guard like Kelechi Osemele is going to get a few bystanders wet.

Besides the Pro Bowler, Oakland also signed pass-rusher Bruce Irvin at the start of free agency. This year, as in 1 p.m. Thursday when free agency officially starts, figures to be a little quieter and not so wet as the Raiders — coming off a 12-4 season and playoff berth — address their needs.

A defensive tackle, linebacker, cornerback and running back top the list. General manager Reggie McKenzie was working Wednesday on re-signing right tackle Menelik Watson and inside linebacker Perry Riley Jr., league sources said. Oakland also would like to bring back defensive tackle Stacy McGee, but indications are he is excited about testing the free-agent market before deciding on a return.

Meanwhile, inside linebacker Malcolm Smith — who started 30 games in Oakland the past two seasons — reportedly will change Bay Area teams and sign with the 49ers, and running back Latavius Murray is being allowed to hit the market with all signs indicating he won’t be back.

No one is saying that out loud, mind you.

“I wouldn’t close the door prematurely on anybody,” head coach Jack Del Rio said last week at the NFL combine.

Murray’s presumed departure, along with the presence of the biggest and one of the best offensive lines in the league, makes Oakland a desirable location for running backs. And it seems like a day doesn’t go by when Adrian Peterson’s agent or dad isn’t telling a national reporter how much he likes the Raiders.

Oakland is intrigued by Peterson — who wouldn’t be with a future Hall of Famer? — but a deep free-agent market and running-back class in the draft likely means McKenzie won’t rush to make a decision here. Paying a running back — especially one who turns 32 next week — a lot of money is not something that the GM really believes in doing, anyway. Giving an incentives-heavy deal to former Green Bay heavyweight Eddie Lacy might be more to his liking.

No, the first order of business is improving a defense that somehow finished last in sacks despite having Defensive Player of the Year Khalil Mack and Irvin. The Raiders need more push up the middle, as well as tight ends and receivers not running free — thus the needs at linebacker and cornerback as well.

The Raiders have $43 million in salary-cap space, ninth most in the NFL, but some of that money is going to go to quarterback Derek Carr’s extension. His agent and the Raiders have talked, but neither side in a rush, and it looks like that will get done after free agency. (Mack’s extension can be done even later, as he was a first-round pick and Oakland can exercise his fifth-year option in 2018 for roughly $13 million).

Ideally, the Raiders would have splurged on former Arizona defensive lineman Calais Campbell, who had eight of his 56.5 careers sacks last season. But ESPN reported Wednesday night that Campbell, 30, will sign with Jacksonville.

Oakland, meanwhile, is monitoring the situation with former first-round pick Nick Fairley, who may re-sign with the Saints. He signed a one-year prove-it deal last year and came up big with 6.5 sacks.

The Raiders did somewhat address their depth on the front line Wednesday by giving restricted free agent Denico Autry a low-round tender (worth roughly $1.8 million). He had three sacks in each of the past two seasons and showed a knack for blocking kicks. Because Autry wasn’t drafted, any team can extend an offer sheet and won’t have to give up a draft pick as compensation if the Raiders don’t match it.

On the offensive line, the Raiders have been trying to re-sign Watson, whom assistant coach Mike Tice loves despite a history of injuries. Watson beat out Austin Howard for the right-tackle job last year, but then went down with a groin injury. He has missed 21 of 48 games in his career, but is a former basketball player with a mean streak.

The Broncos reportedly are interested in signing him if the Raiders let him hit the market.

Vic Tafur is a San Francisco Chronicle staff writer. Email: vtafur@sfchronicle.com Twitter: @VicTafur

Raiders’ to-do list

DT: The Raiders could add Nick Fairley in free agency. He got some pressure on quarterbacks last season in New Orleans.

LB: Sounds like the Raiders are trying to bring back Perry Riley, but more help is needed inside. Buffalo free-agent Zach Brown would give them the cover man they haven’t had.

CB: It wouldn’t be shocking if they brought back DJ Hayden, but they can do better. Starters Sean Smith and David Amerson each can improve on last season.

RB: Former Packer Eddie Lacy would make a lot of sense as a bigger back to go with Jalen Richard and DeAndre Washington. Or Reggie McKenzie could wait until the draft.

WR: The Raiders love Andre Holmes, but aren’t sure they want to lock up the No. 4 spot when other options are out there. Pipe-dream slot receiver DeSean Jackson is going to get too much money, probably in Tampa Bay.

— Vic Tafur