Bielsa warned that the delay in bringing Brown into the first team ranks “won’t be a short time” as Brown continued the process of regaining full fitness after a serious knee injury.
The 21-year-old underwent surgery on a damaged ACL in January and only resumed training with Chelsea last month.
Leeds nonetheless signed him a day before the transfer deadline, striking a season-long loan in the hope that Brown would provide cover from playmaker Samuel Saiz at a later stage of the campaign.
The club planned to put him through a mock pre-season and Bielsa, whose squad have been affected by a series of injuries over the past six weeks, said he could not predict when Brown would be ready to feature in the Championship.
United’s head coach saw Adam Forshaw return from a broken foot at Millwall on Saturday and is hopeful that Gaetano Berardi and Jamie Shackleton with return from knee and ankle problems in the days to come.
Kemar Roofe is carrying a calf problem and Pablo Hernandez is nursing a hamstring strain, ruling both players out of tonight’s clash with Preston North End. Patrick Bamford, meanwhile, has been sidelined until after Christmas with a knee problem.
Asked if Brown was close to a comeback, Bielsa said: “It’s a very different case. It’s been a long time since he played. He still needs to recover.
“He hasn’t started to play with the ball, he hasn’t played football with us so far. It’s impossible to say when he’ll be fit. It won’t be a short time.”