BEREA (AP) — The sturdy left side of Cleveland’s offensive line has developed a massive hole.

Guard Eric Steinbach’s season is over.

The steady Steinbach, who hasn’t missed a snap in two years at left guard, was placed on injured reserve Tuesday, hours after undergoing surgery to repair a bulging back disk. Steinbach’s back stiffened up during practice two weeks ago, and when it didn’t respond to treatments, the eight-year veteran opted for surgery.

Browns coach Pat Shurmur said Steinbach’s operation went well, but the Browns had no choice but put him on IR, a major loss for their offense.

“He’s been incredibly durable,” said Pro Bowl tackle Joe Thomas, who has lined up for 62 of his 64 career games alongside Steinbach. “He’s been a huge asset to our offense, so it is a big blow not having him out there.”

Cleveland’s left side is arguably the NFL’s finest with Steinbach sandwiched between Thomas, a four-time Pro Bowler, and center Alex Mack, chosen to go to Hawaii last year following his second season as a pro. Steinbach’s loss will not only hurt the Browns’ running game and ability to protect quarterback Colt McCoy, but it may force Shurmur to start rookie Jason Pinkston up front in the Sept. 11 season opener against Cincinnati.

“I wouldn’t presume anything right now,” Shurmur said, “but if we were playing a game tomorrow, that’s what we would probably do.”

Shurmur indicated the Browns would explore other options, especially with teams trimming their rosters before Saturday’s deadline to get to 53.

“There’s a lot of things that get done now in the next 48 or 72 hours,” he said.

Replacing Steinbach won’t be easy.

The 31-year-old has been rock-solid since joining the Browns in 2007 as a free agent after playing four seasons with the Cincinnati Bengals. He made 65 consecutive starts before missing two games in 2008, but was out there for every play the past two years under coach Eric Mangini.

Steinbach’s quickness allowed the Browns to use him on sweeps, and his outside, pulling blocks helped Peyton Hillis rush for nearly 1,177 yards and 11 touchdowns last season.

Thomas hates to lose his left-side partner, but in this league there’s no time for sympathy.

“It’s the next-man-in mentality,” Thomas said. “We’ve gotta have somebody step up there. Hopefully it’ll be Pinkston.”

A fifth-round pick who played left tackle at Pittsburgh, Pinkston has already been thrown into the pool’s deep end. Now, he has to keep himself afloat.

“That’s why they draft you,” the 6-foot-4, 305-pounder said. “They bring you in here and you’ve got to be ready, because you know it’s a long season. You never know when someone’s going to get banged up or nicked up or what’s going to happen. You just got to be ready to step up and play.”

Thomas can appreciate Pinkston’s situation. After being drafted third overall in 2007, he started right away and had to learn on the fly. Not every rookie can do it, and it’s even tougher for Pinkston because of the NFL lockout and because the Browns are implementing a new offensive system.

“It’s definitely an uphill battle, especially for a rookie,” Thomas said. “It would be an uphill battle for anybody who didn’t get all the reps in a new offense with a new coach and everything like that. We’ll get him ready for that first game, whoever it is.”

Pinkston admitted playing alongside a pair of Pro Bowlers can be a bit intimidating, and there have been times he’s felt lost before the ball is snapped. It’s at those moments when he turns to Thomas or Mack.

“Sometimes I come up there and I freeze a little bit,” Pinkston said. “Joe leans over, ’You know what you’re doing?’ he helps me out. Or Alex. They’ve been great with helping me out. No complaints there.”

If Pinkston can’t get the job done, the Browns have other options.

On Tuesday, they added depth when they were rewarded Oneil Cousins off waivers from Baltimore. Cousins, a former third-round pick, lined up at right tackle with the second-string offense in practice. Also, the team acquired veteran guard John Greco earlier this month in a trade with St. Louis.

Thomas said Steinbach’s replacement has big shoes to fill, and that there isn’t much a team can do to hide a player.

“You’d hope that whoever steps in there is going to be able to hold his own and it’s not going to have to be somebody to cover up,” he said. “But there’s plenty of different schemes you can run to try to help certain guys.”

Notes: TE Ben Watson missed his second straight practice with a hip injury. … Starting right tackle Tony Pashos was also kept out of some drills, but Shurmur said the big man “was fine.” … The Browns will fly to Chicago on Wednesday for Thursday’s preseason finale. Shurmur said he’s still trying to decide how much playing time to give his starters, but hinted he will probably rest most of them.