Sakho will wear the number 10 shirt this season. Didier Domi will wear number 29, last worn by ex-captain Rio Ferdinand.
Meanwhile, Peter Reid has completed the loan signing of French defender Joel Sammi. Central defender Sammi has impressed Reid during his spell on trial at Elland Road this summer, enjoying an eye-catching 'debut' in the 0-0 friendly at Bristol City.
The Leeds boss had earmarked the centre of his defence as a particular weak area this summer, but following the earlier loan capture of Zoumana Camara from Lens, Reid will now feel he has sufficient cover after reaching a similar agreement with French side Valence for Sammi.
The 18-year-old is not expected to be a regular this term, but will provide valuable back-up for Camara, Lucas Radebe, Dominic Matteo and Michael Duberry.
United will learn on Saturday their opponents in the Carling League Cup second round next month.
It is the first time Leeds have been involved in the second round draw for six years as European football has usually been par for the course during this period.