Blackman suffered a fractured tibia in the Whites’ under-23s clash with Birmingham City on Friday afternoon.
Carlos Corberan’s men fell to a 3-0 defeat at Thorp Arch with Blackman suffering the injury in the closing stages of the game following a collision with City forward Beryly Lubala.
The 25-year-old left the field of play on a stretcher after picking up what appeared to be a right leg injury.
Leeds have since confirmed the extent of the issue with Blackman now returning to parent club Chelsea for his rehab.
United defender Hugo Diaz saw out the final minutes in goal with Leeds having used up all three substitutions.
There was good news though for fellow Chelsea loanee Izzy Brown as he completed 45 minutes in the same outing.
Brown, who joined the club on a season-long loan in the summer, picked up the injury whilst on loan at Premier League side Brighton & Hove Albion in January after just six minutes of their FA Cup clash with Crystal Palace.
The attacking midfielder joined the Whites despite still needing to complete his rehab with Leeds working closely to monitor his progress alongside parent club Chelsea.
Brown’s deal also included a clause where Leeds would only contribute towards his weekly wage once he was back fit and available for first-team selection.
The 21-year-old came through the opening 45 minutes unscathed before being replaced at the break by Clarke Oduor.
Two goals from Omar Bogle and a converted penalty kick from Craig Gardner settle the tie as United fell to a disappointing defeat.
It was a second defeat in a row for Carlos Corberan but only the third of the season in the Professional Development League.