Douglas damaged a medial ligament in Saturday’s 3-2 win over Millwall and has been sidelined for up to 12 weeks, taking his recovery period beyond the end of the Championship term.
The defender left Elland Road in a leg brace on Saturday evening and was sent for scans yesterday. The results revealed that Douglas would be absent for at least two months.
He was hurt in the second half against Millwall at a time when Marcelo Bielsa had already used all three of his substitutions.
The former Wolverhampton Wanderers player continued until full time to prevent Leeds suffering a numerical disadvantage but was in obvious pain throughout.
Douglas - a £3m summer signing from Molineux - is on the verge of a second promotion in two seasons having been part of Wolves’ title-winning squad last year.
The second half of his first campaign at Leeds has been badly affected by injury, however, and Bielsa will be without him for the last seven matches and the play-offs if United finish below the top two.
Bielsa had hoped to have a fully-fit squad available for the first time at Birmingham City this weekend with Kemar Roofe on the way back from a knee injury.