Harrison was smacked in the eye by the helmet of Texans left tackle Duane Brown during an open-field block with just under six minutes left in the first half. Harrison left the field, but returned to play the fourth quarter.
"He's James Harrison," was how Tomlin explained it at his Tuesday press conference.
Tomlin won't have Harrison's backup, Jason Worilds, available either. Worilds is doubtful with a left quadriceps strain, so Tomlin will move Lawrence Timmons from the weakside inside linebacker position (mack) to right outside linebacker and insert Larry Foote into the mack, where he started from 2004 through 2008 for the Steelers.
Timmons made two starts at outside linebacker during the 2008 season.
Tomlin did have some good news on the injury front. An MRI of Ben Roethlisberger revealed only a sprain of his injured left foot.
"It may limit him in the early portions of the week but we anticipate him being able to play in this football game," Tomlin said of Sunday's home game against the Tennessee Titans.
Last season, Roethlisberger had to wear a protective shoe on his right foot after tearing scar adhesions on an old injury.
If Roethlisberger doesn't recover as expected this week, Tomlin said the Steelers will have "a package of plays ready for Charlie Batch."
Tomlin also listed three players as questionable for Sunday: RB Mewelde Moore (left ankle sprain), DE Aaron Smith (right mid-foot sprain) and rookie CB Cortez Allen (right ankle sprain). Tomlin added that Smith was "extremely questionable."
Noting that both Mendenhall and Moore could "at the very least be nursing injuries," Tomlin said Isaac Redman will receive the bulk of the work in the early part of the week and "we expect Jonathan Dwyer to be ready."
Tomlin also said the team would like to add a practice back this week to simulate Titans speedster Chris Johnson.
Expected to return to the practice field this week are recovered Steelers DE Brett Keisel, LT Jonathan Scott, RG Doug Legursky and CB Bryant McFadden. All but McFadden are expected to start Sunday's game. McFadden may start if he proves superior to William Gay in practice.
Keisel has missed the last two games with a sprained posterior cruciate ligament and the Steelers have allowed 4.9 yards per carry, including a 155-yard performance by Arian Foster in Houston.
But with Keisel in the lineup, the Steelers allowed 4.7 yards per carry.
Overall, the Steelers rank 23rd in the NFL in run defense. They allow 119.5 yards per game and 4.8 per carry a year after allowing 62.8 and 3.0.
"As far as how we've defended the run of late, that has nothing to do with Brett Keisel's absence," Tomlin said. "We have capable men who play and who need to do a better job."
Tomlin was asked whether the problem had to do with players missing gap assignments or being physically overmatched.
"It's been a little bit of both," he said. "They're not centrally located in one person or position."