Flo has been troubled by foot injuries ever since his move to United in January, and his latest set-back could rule him out of contention for the foreseeable future.
Flo is one of three players unavailable for tomorrow's League One clash with Yeovil Town at Elland Road.
Leon Constantine and Shaun Derry are long-term absentees, but Dennis Wise has not been able to call on either players this season and he will pick from a familiar squad this weekend.
Tresor Kandol and Jermaine Beckford are returning from one-match bans, meaning Mark De Vries and Wayne Andrews are likely to drop out of United's starting line-up after their debuts at Oldham on Tuesday, but Wise's two changes up front may be his only alterations.
The Whites (from): Ankergren, Richardson, Heath, Marques, Huntington, Hughes, Clapham, Parker, Prutton, Thompson, Douglas, Carole, Westlake, Howson, Weston, Beckford, Kandol, De Vries, Andrews, Ameobi, Lucas, Martin.