The Riders have won just two league games out of 11 and last weekend went out in the first round of the National Cup.
Harris, a former England international, Riders player, and assistant coach, is taking a hard line in his rookie season in charge.
"We only start playing when we're behind, and then it's too late," he said. "We've seen videos of several players who want to come here. If our current players don't start to make things happen, there will be changes."
London Towers and Leopards meet for the first time this season tonight, occupying sixth and eighth place in the table, and unsure of even qualifying for home advantage in the play-offs.Reuse content