The Vikings appear to have settled on Joe Berger as their starting center, making John Sullivan, one of the team’s longest-tenured players, expendable.

A day after Sullivan did not play in a 23-10 preseason win over the San Diego Chargers, the Vikings attempted to trade Sullivan, an NFL source confirmed.

They were unable to complete a deal on Monday night, and if they can’t by Tuesday’s 3 p.m. deadline for teams to cut their rosters down to 75 players, the Vikings could release Sullivan, who has been with the team since 2008.

That means that Berger, who was the only center to snap the ball to starting quarterback Teddy Bridgewater during Sunday’s win, likely will be the Week 1 starter with second-year center Nick Easton behind him on the depth chart.

Sullivan, 31, missed the entire 2015 regular season after twice undergoing back surgery. He was cleared to return for the start of spring workouts. But the Vikings informed him that he would have to reclaim his old job from Berger, the 34-year-old who played well last season while starting every game at center.

During the first week of training camp, Sullivan and Berger alternated days as the first-team center in practice. When right guard Brandon Fusco was in and out of the lineup due to a shoulder injury, Berger slid over to right guard and started the first two preseason games next to Sullivan, the starting center.

Sullivan, who still is trying to get back to full strength after being idle for much of last fall, got shoved around at times during training camp and the two joint practices with the Cincinnati Bengals. But he performed better at center in the team’s first two preseason games against the Bengals and Seattle Seahawks.

In all, Sullivan and Berger each spent the majority of practice with the starters during 13 of the team’s 21 practice days this summer. Sullivan spent all 13 at center while Berger was at center for eight practices and right guard for five.

Coach Mike Zimmer explained that Berger played the entire first half vs. the Chargers because the Vikings wanted to see him play center in the preseason. Berger clearly answered any remaining questions they had about his ability to start.

Easton, whom the Vikings acquired from the San Francisco 49ers last October, was the second-string center in Sunday’s win. The coaches like his athleticism, smarts and competitiveness and have felt he is a prospect worth developing.

Third-year offensive lineman Zac Kerin, who has mostly lined up at guard this summer, can also play center if the Vikings opt to include him on their 53-man roster Saturday when the NFL requires teams to make their final roster cuts.

And since Sullivan is strictly a center, one with a $5.4 million base salary that would be a lot to pay a backup, the Vikings started to shop him to other teams. If the Vikings trade or release Sullivan, they will free up $5.2 million in salary cap space while incurring less than $700,000 in dead money on next year’s cap.

The Vikings drafted Sullivan in the sixth round of the 2008 draft and the Notre Dame product took over for Pro Bowl center Matt Birk a year later. He missed only three games over the next six seasons, beginning in 2009, while starting 93 games.

In April 2015, the Vikings extended his contract through the 2017 season and gave him a raise. Five months later, he underwent back surgery for the first time.

While waiting to see if they could find a taker for Sullivan, the Vikings informed several players they would be released during the first wave of roster cuts. One of them, according to a league source, was offensive tackle Austin Shepherd, who appeared in 14 games as a rookie in 2015 and was often their sixth offensive lineman in heavy sets.

The Vikings are also parting ways with tight end Brian Leonhardt, a league source confirmed, after getting good news about tight end MyCole Pruitt, who only suffered a sprained MCL in Sunday’s game and will be sidelined two to four weeks, per another league source.

matt.vensel@startribune.com mcraig@startribune.com