The Frenchman is likely to be out for a minimum of four weeks after suffering an injury in Saturday’s 1-0 win over Middlesbrough.
The 22-year-old - one of United’s 10 summer signings - was hurt by a late tackle from Boro left-back George Friend shortly before half-time.
Leeds substituted him early in the second half and Doukara was seen wearing a protective boot during Tuesday’s 2-0 defeat to Brighton.
Head coach David Hockaday said: “He’s ruptured his ankle ligaments. It was a really bad tackle and he’s going to be out for weeks.
“It’s a blow because we need more pace and Souley gives us pace and the power. We missed him (against Brighton). It’ll be X number of weeks for him, not just one or two. How many will depend on how it settles down but I’d think three or four weeks minimum.
“He doesn’t need an operation, he’ll get an injection which will tighten everything up and hopefully speed up the healing process.”