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The Steelers defense will find out what life is like without James Harrison.

Coach Mike Tomlin announced Tuesday that Harrison will undergo surgery Wednesday on a fractured right orbital eye socket. Tomlin said Harrison would be out a “number” of weeks.

Harrison explained on Twitter: “My forehead pad in my helmet came down and hit me in the eye when I made contact with the tackle.”

With Harrison’s backup Jason Worilds also iffy to play, Tomlin indicated that Lawrence Timmons will move to the outside with Larry Foote replacing Timmons inside.

The Steelers’ defense has looked up-and-down thus far this season. The overall numbers don’t look bad, but the Ravens and Texans ran right through them. Tomlin indicated the team may practice in pads a few times this week.

It’s rare that a Ben Roethlisberger injury isn’t top news, but that was the case Tuesday. Tomlin indicated that Big Ben would likely be limited in practice early in the week because of his foot injury, but he should “round into shape” by the weekend.

While Tomlin wouldn’t say it outright, it sounds like there is little doubt Roethlisberger will face the Titans.

Running back Rashard Mendenhall is far less likely to play. If he’s out with a hamstring injury, Tomlin confirmed Isaac Redman will start and take the majority of work. Third down back Mewelde Moore is also hurt.

Defensive end Aaron Smith has a mid-foot sprain and Tomlin seemed unsure if he’d suit up.