Both players left the court holding towels over their faces, and both needed stitches.
"They both have headaches," Magic spokesman Joel Glass said.
"They hit pretty hard. We'll just see how they feel in the morning
and go from there."
Coach Brian Hill said Nelson "got the worst of it."
"We're worried about his head ... about headaches and stuff," he told the Orlando Sentinel.
Howard, 6-foot-11 and 268 pounds, was crouched low with the ball when Nelson, 5-10 and 190, curled around him chasing Travis Diener. Howard and Nelson then crashed into each other.
The Magic already were missing guard J.J. Redick (left foot).