Harrison says Roebuck is not being rushed back into action, and he is confident the switch will not adversely affect England’s prospects.
“In an ideal world we’d have given him an extra week, but the world isn’t ideal as we know,” Harrison said.
“We do a really good job of ‘what ifs’ and what might happen and combinations.
“Does it disrupt some plans? Yes it does, because it’s changing a player. But we’ve done everything we can to make sure the next player is ready.”
For Feyi-Waboso, of Exeter Chiefs, it is the second time injury has affected his Six Nations hopes.
Shortlisted for World Rugby’s Breakthrough Player of 2024 award, a shoulder injury meant he missed last year’s competition.
He made his return to rugby in an England A game against France but was red-carded for a high shot on Antoine Hastoy.
A ban ruled him out of two Tests against Argentina in the summer, but he returned to the starting line-up against the United States in July.
Aiming to win their first Six Nations title for six years, England go into the competition on a run of 11 wins and their first unbeaten four-Test autumn in nearly a decade.