Hassan, 23, averaged 12.6 points and 5.8 rebounds per-game for the Savannah State Tigers last season.
Coach Rob Paternostro told BBC Radio Leicester: "We watched a lot of players and liked what he was able to do. We feel his best days are ahead of him."
Hassan told the club website: "I'm excited and don't feel pressure. as I'm coming to a focused and great team."
He added: "I'm thankful for the opportunity to play pro basketball and I'm ready to begin playing for the Riders.
"It really wasn't a tough decision, because I was happy about coming to a winning organisation."
Paternostro, who led the Riders to win the treble of the BBL play-off final, the BBL Cup and BBL Championship last season, has signed a new long-term contract with the club.
He has also resigned Barry Lamble, Drew Sullivan, Anthony Rowe and Jay Cousinard ahead of next season.
Source: http://www.bbc.com/sport/basketball/23285002