Aksalu, 25 joins from his native Estonia for a nominal fee and could be in line to feature at the Hawthorns tomorrow, though is likely to only make the bench at most with the inform Mark Bunn most likely to start.
Blades boss Kevin Blackwell said; "It is a terrific opportunity for him and if he continues his development he will become the number one Estonian goalkeeper. We are hoping he can fulfil his undoubted potential with Sheffield United and cement his international career."