The 21-year-old, who has attracted interest from Middlesbrough in recent weeks, had been expected to make a major impact on the first team this season after impressing in pre-season.
Darius suffered his knee injury because of an intense traing regime on hard pitches, damaging his fragile knees that had already had to be rested over the summer months.
"Since returning from his ankle injury Darius has had some problems with the recurrance of a knee injury, due to the hard ground and the intensity of some of the training sessions," explained physio Jon Fearn, speaking to readingfc.co.uk.
"The knee hasn't settled down so we'll have to pull him out of training for a few weeks. We're estimating that it'll be three or four weeks but it'll be as long as it takes.
"It's Darius' decision as much as mine. He didn't feel he was doing himself justice, and it was playing on his mind, so it's wise to get it sorted at this time."