Harrison's agent, Bill Parise, believes Harrison still might be ready for the Sept. 9 opener against the Broncos in Denver if the former NFL Defensive Player of the Year has to have arthroscopic surgery.
According to Parise, the Steelers plan to remove Harrison from the physically unable to perform list in the next two weeks. If the swelling continues after he practices on the field, he will be shut down to undergo the procedure.
Harrison, 34, has dealt with an inflamed knee since minicamp this spring and has been on the PUP list for more than two weeks.
"With the exception of this little knee thing, James is probably healthier now than he's been in three years," Parise told the newspaper. "He's extremely fit. He just has to get this irritation behind his kneecap cleared up. That's what's causing the swelling, and (the Steelers) just want to get rid of that. ... We'll just have to wait (and) see how it plays out."
Meanwhile, Steelers running back Isaac Redman said he will have an MRI on Thursday morning for his groin injury. He is uncertain whether he'll play in Sunday's preseason game against the Colts.
"It hurts a little," Redman said. "It's tough to run right now."
Redman is in his first year as the Steelers' starting running back, filling in for Rashard Mendenhall, who is on the physically unable to perform list. Redman's MRI was news to offensive coordinator Todd Haley.
"You guys have more information than I do right now," Haley said. "We're not trying to put too much on him because he is a little bit nicked up. But the way I understood it, we're going to stay on course with the plan to get him some carries in this game."