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Caldwell hasn’t decided what he’ll do in Sunday’s preseason opener against San Francisco.

Traditionally, the Colts play starters about 10 plays in the first preseason game, but a suddenly thin offensive line could change the script.

Saturday has missed three consecutive days of practice with his injury.

Left tackle Charlie Johnson, the man responsible for protecting Manning’s blind side, was carted off the field during Friday’s practice and hasn’t been seen since. He has a sprained right foot, and the Colts haven’t said when Johnson will return though Caldwell acknowledged Johnson was getting better.

Right tackle Ryan Diem has skipped the three morning workouts this week after his wife delivered the couple’s first child.

Rookie guard Jacques McClendon, a fourth-round pick, has been out all week with an undisclosed injury and things were so bad that the Colts have brought in reinforcements the last two days.

They released guard Andy Alleman after the veteran hurt his back, replacing him with undrafted rookie James Williams on Tuesday morning. They also added center Adrian Martinez, claiming the rookie off waivers from Seattle.

“I told the guys there would be some adversity in training camp,” Caldwell said. “The best thing is if you can come out of camp with a little more experience and depth, and we’ve had that happen before. We hope that can happen again. But we’ve got to keep on getting better. No excuses, just keep getting better.”

The Colts expect nothing less.

“It’s tough, he (Saturday) is the foundation of our offensive line,” Pro Bowl tight end Dallas Clark said. “What he brings is consistency, his level of play, all those intangibles are just invaluable. It’s definitely the next-guy-up theory, but it’s going to be tough without him.”