Ex-Giants guard expected to sign with S.F.

The 49ers will begin free agency by tackling their trenches.

After allowing the 10th-most sacks in the NFL last year, many because of pressure up the middle, the 49ers are expected to sign former Giants center/guard Weston Richburg to a five-year contract when free agency officially starts Wednesday, ESPN reported.

Richburg, 26, is a secondround pick who was the fourth interior offensive lineman selected in 2014. He played in 47 of 48 games (46 starts) in his first three seasons before sustaining a concussion last year that limited him to four games. After Richburg was injured in Week 4, he was sidelined for three weeks before he was placed on injured reserve Nov. 4.

On Jan. 1, Richburg told reporters he’d been medically cleared “three or four weeks” earlier.

“I wanted to play,” he said. “But that’s just the way it turned out this year.”

Given his versatility, there is a question where Richburg will play with the 49ers. He played left guard as a rookie before starting at center the past three seasons. After struggling at guard, Richburg blossomed at center from 2015-2016, according to Pro Football Focus’ grading system. He ranked third in their pass-blocking efficiency among centers each season.

In February, the 49ers signed center Daniel Kilgore, 30, to a three-year extension that includes $4.8 million guaranteed in 2018. Head coach Kyle Shanahan recently told reporters at the NFL combine that Kilgore is expected to be the starting center.

However, Kilgore has also played guard in his seven-year career and the 49ers’ new regime didn’t anoint him the starting center after they arrived last year. In March 2017, they traded for Ravens center Jeremy Zuttah, who had been a Pro Bowl alternate the previous season, and later signed center Tim Barnes. Both were beaten out by Kilgore and cut before the start of the regular season.

The 49ers’ situation at guard is unsettled. Last year, their starters were Laken Tomlinson, a former first-round pick acquired in an August trade with the Lions, and Brandon Fusco, who is a free agent.

They also have Joshua Garnett, a 2016 first-round pick who missed last year after undergoing knee surgery before the season. Garnett, who is listed at 6-foot-5 and 321 pounds, could have returned last year, but the 49ers opted to give him a redshirt season. Garnett used the time to drop weight and reshape his body to become a better fit in a zoneblocking scheme that requires quickness from offensive linemen.

Given that, Richburg (6-4, 300), who is relatively undersized, is a logical fit for the 49ers’ front.

Meanwhile, the 49ers are looking to add depth to a cornerback corps bolstered by the signing of Richard Sherman on Saturday. They have a freeagent visit scheduled Wednesday with DeShawn Shead, 28, the NFL Network reported. Shead visited the Lions on Tuesday.

Shead was released by the Seahawks on Monday after he missed the first 14 games of last year with a torn ACL. Shead played on special teams in the final two games of last season.

In 2016, Shead made 15 starts alongside Sherman. Shead, who has the size 49ers defensive coordinator Robert Saleh seeks at 6-foot-2 and 212 pounds, has two picks and 24 pass break-ups in his 22-start career.