The 19-year-old's spell at Bramall Lane will extend to cover the playoffs, should the Blades finish in a qualification spot.
The forward scored twice during an eight-match loan stint at League One side Bury earlier this season, and United boss Danny Wilson cannot wait for Poleon to link up with the club.
"He's young. He's raw and unpredictable but very quick - he can get in behind the back of people and he can get a goal," Wilson told BBC Sport.
"We just feel he can add a little bit extra from the bench or even start."
Poleon recently signed a new two-and-a-half-year deal at Elland Road.