Harris didn't take part in Tuesday's walkthrough due to a knee injury, Teresa Varley of the Steelers' official site reports.
Harris wasn't included on Pittsburgh's practice estimate Monday, so his addition one day later is somewhat concerning ahead of Thursday's game against the Patriots. He hasn't missed a game in his two-plus seasons as a pro, however. If Harris is limited or sidelined Thursday, Jaylen Warren could take on a workhorse role for the Steelers.