The midfielder missed Easter Monday's Premier League clash against Norwich City with tight hamstrings, having played at Sunderland on the Saturday.
"Scott's fine," said Harry. "His hamstrings were tight after game at Sunderland and he felt he might tear a hamstring if he played against Norwich. That was a chance I couldn't take."
Unfortunately, Younes Kaboul and Niko Kranjcar are now sidelined with knee injuries - ruling both out of Wembley.
Younes had to be substituted in the first half against Norwich while Niko suffered his problem in training this week. "They won't be available this weekend and we've one or two knocks as well," added Harry.
Michael Dawson and Tom Huddlestone remain out as they recover from longer-term ankle injuries.