Mike Tomlin dealing with injuries to Steelers starters Cameron Heyward, Diontae Johnson

Depth along the defensive line was considered so abundant for the Pittsburgh Steelers that one player they signed in free agency didn’t make the 53-man roster, and another was inactive for the season opener.

Earlier than they anticipated, the Steelers will see just how deep they are on the defensive front after coach Mike Tomlin confirmed Tuesday that team captain and 13-year veteran Cameron Heyward will need surgery to repair a groin injury.

Heyward, who at 34 is the team’s oldest player, is a candidate to be placed on injured reserve, which would require him to sit out at least four weeks. The injury, which occurred in the first half of the Steelers’ 30-7 loss Sunday to the San Francisco 49ers, is the first for Heyward since 2016.

Tomlin also revealed that wide receiver Diontae Johnson is unlikely to play Monday night against the Cleveland Browns because of a hamstring injury. Elsewhere on the defensive line, Larry Ogunjobi remains bothered by a foot injury that kept him from playing in the preseason, and second-year lineman DeMarvin Leal left the opener briefly with an elbow injury.

Leal will be one candidate to take Heyward’s spot on the defensive line. Isaiahh Loudermilk and second-round draft pick Keeanu Benton are others who saw defensive snaps against the 49ers.

“Obviously, losing Cam is significant, but that is what team is about,” Tomlin said Tuesday at his weekly news conference. “Replacing Cam is not a one-man job. It is a multiple-man job and a coach’s job. It changes your schematics when you lose significant players. We all acknowledge that.”

Heyward played just 14 of 68 defensive snaps against the 49ers, who exploited the Steelers defense by rushing for 188 yards. The Steelers rotated five other players along the front, with Ogunjobi logging the most snaps (43) in spite of his foot injury.

Nose tackle Montravius Adams (34 snaps), Loudermilk (31), Benton (29) and Leal (26) also saw significant playing time.

Loudermilk, who is in his third season, and Leal could take on larger roles at defensive end.

“I’ve been really impressed with the growth and development and what those guys have shown me in team development,” Tomlin said. “Not only Loudermilk, but younger guys like Benton and others. I thought that was one of our strengths coming out of team development: depth and competition and tough decisions we had to make on the defensive line.”

After keeping Ogunjobi from hitting the open market in free agency, the Steelers added former Minnesota Vikings and Chicago Bears defensive tackle Armon Watts and former Los Angeles Chargers nose tackle Breiden Fehoko.

Watts earned the final spot on the 53-man roster but was inactive against the 49ers. Fehoko was cut but re-signed to the practice squad.

In the draft, the Steelers used their second pick of the second round to select Benton.

“This is an opportunity to show what team is about,” Tomlin said. “Things we hold near and dear like ‘next man up.’ We have an opportunity to make it real when faced with adversity that comes with attrition in the game. That is our mindset.”

Heyward hasn’t missed a game since a torn pectoral muscle injury landed him on injured reserve for the second half of the 2016 season. Since returning from that injury, he has made the Pro Bowl in six consecutive seasons and earned three All-Pro selections.

“It’s very tough,” inside linebacker Kwon Alexander said. “Cam is very tough, a veteran who has been in the league a long time and knows how to play the game well. We have guys who have to step up and get ready for action.”

That holds true at wide receiver after Johnson’s exit early in the second half against the 49ers.

Johnson has missed only two games in his five-year career, and he played in all 17 games last season. ESPN reported that Johnson could be out “a few weeks.”

Tomlin wouldn’t go that far.

“It’s reasonable to expect he won’t be available to us this week,” Tomlin said. “I feel capable about our in-house people.”

Gunner Olszewski, who was inactive against San Francisco, is expected to take Johnson’s roster spot against the Browns and join the receiver trio of Allen Robinson, George Pickens and Calvin Austin III.

The Steelers also are dealing with injuries to three other offensive starters: tight end Pat Freiermuth (chest), right tackle Chuks Okorafor (concussion) and right guard James Daniels (foot). Tomlin said they could be limited in practice this week.

Because they play Monday night, the Steelers have an extra day of preparation.

“We’ll definitely take it,” Tomlin said.