Raiders left tackle Donald Penn is expected to end his 25-day holdout and return to practice this week, according to league sources. He was not on the field for the start of practice Tuesday.

Penn missed all of training camp in Napa, seeking a substantial raise from his 2017 salary of $5.95 million.

That isn’t going to happen — not yet, at least, as negotiations might pick up once Penn returns — but he probably will get that salary guaranteed for at least this season. Penn, 34, made the Pro Bowl last season and is entering his fourth year with Oakland, his last on his second two-year deal.

At 6-foot-4, 330 pounds, Penn has a very important role on the Super Bowl contender: He is Derek Carr’s bodyguard. Saturday’s preseason game against the Rams was the first in the NFL that Carr has played without Penn.

Carr said he has talked to Penn regularly during the holdout, but he declined to get into the tackle’s business affairs.

“Obviously, he’s our teammate. We love him,” Carr said after Saturday’s game. “We want all of our teammates here. When it comes to another man’s situation, I just stay out of it.”

General manager Reggie McKenzie also professed his love for Penn but said he wanted the tackle to honor his contract, and McKenzie said he wouldn’t negotiate with a player who wasn’t at camp.

Coming back makes a lot of sense for both sides. Penn can get ready for the third preseason game Saturday and the start of the regular season Sept. 10. Missing camp wasn’t that big of a deal, considering that Penn is in great shape and would have received a handful of days off to save his legs.

Penn kept busy while he was gone, working with offensive-line specialists, including esteemed private coach Duke Manyweather, who posted the workouts online. Penn knows that despite his age, he could earn a big contract next year by playing well this season.

Penn was (and still is) hoping for a raise now, after outperforming his two-year, $11.9 million deal last year. He wants to be among the league’s best-paid left tackles; his salary ranks 23rd, according to the contract-tracking website spotrac.com. The Rams’ Andrew Whitworth is No. 10 at $11.25 million.

Penn did not talk to reporters on the record during the holdout, but he did allow NFL Network analyst and former New England linebacker Willie McGinest to speak for him at the start of training camp.

Penn “just wants the respect for what he’s done on the field,” McGinest said. “Stop looking at his age; look at his production.”

A 34-year-old player has to take whatever shot he has at more money, and Penn saw leverage after Oakland gave Carr a league-record $125 million extension and brought running back Marshawn Lynch out of retirement.

Although the Raiders are under the salary cap even after giving Carr and guard Gabe Jackson hefty extensions, McKenzie wasn’t looking to reward the team’s first holdout since JaMarcus Russell in 2007. And though Penn’s camp said it expressed its unhappiness with the deal three months ago, Raiders officials and coaches say they heard about it only the week before camp and were blindsided by the holdout.

McKenzie also has to be careful about giving too many extensions while defensive end Khalil Mack, the NFL Defensive Player of the Year last season, waits until next year for his payday.

The Raiders had the right to pick up their contract option on the 2014 first-round pick, and Mack is doing his best to be patient — unlike Rams defensive tackle Aaron Donald, another dominant fourth-year player, who is holding out.

As for Penn, his leverage on the field didn’t hold up.

Marshall Newhouse, a seven-year vet signed from the Giants to start at right tackle, did an admirable job at left tackle at training camp and in the first two preseason games. Second-year player Vadal Alexander got the starting reps at right tackle, and rookie David Sharpe hasn’t given up a pass pressure at either spot in two games.

The only sack the Raiders allowed came on the final offensive play Saturday night.

Penn has not missed a regular-season game, but he did miss a chance to play in his first playoff game, after a left knee injury forced him to miss Oakland’s wild-card-game loss at Houston.

Penn gave up only one sack last season, but it was the one that ended Carr’s season (broken leg) in Week 16 against Indianapolis.

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