Union coach Jim Curtin revealed Blake had suffered a groin tear on Wednesday. Curtin declined to give a timetable for Blake's return though he hopes the absence won't be a long one.
Blake picked up the injury during last weekend's 3-0 win over the Montreal Impact, and was forced to exit in the second half.
Meanwhile, Fabian has returned to the training pitch in a limited capacity following an ankle sprain sustained during an April 13 loss to the LA Galaxy, Curtin said.
The Union are next in action on Saturday against the Vancouver Whitecaps (5 pm ET | TSN in Canada, MLS LIVE on ESPN+ in US).