Toppin got tangled with Minutemen forward Samba Diallo at midcourt and went down hard at 15:13 of the second half, grabbing his left ankle. Both players lay on the court for several minutes before walking off, Toppin with a slight limp as he headed for the locker room.
"A sprained ankle is the indication right now," coach Anthony Grant said after the game. "I think the next 24 hours will tell us more in terms of how it reacts."
Toppin had scored 16 points prior to the injury, which came with Dayton up by 25. The sophomore is averaging 19.2 points per game.
Diallo returned to the game a few minutes later. Late in the game, Toppin returned to the bench with a protective boot on his left foot and watched the final minutes.
"It was good to see him able to walk on his own power back to the bench," Grant said.
Dayton (14-2, 3-0 A-10) hosts VCU (12-3, 2-0) on Tuesday.
The Associated Press contributed to this report.