The Cottagers were trailing 1-0 as half-time approached, following Ahmed Elmohamady’s headed opener, when Bettinelli rushed of his line to stop Abel Hernandez from doubling the lead.
While the former England Under-21 international managed to make a fingertip save from Hernandez’s flick, the Fulham goalkeeper and team-mate Smith accidentally collided each other.
Bettinelli was stretchered off the field and striker Smith was also substituted although it is the former’s blow that could turn out to be the more serious.
“Both Marcus and Matt have got knee ligament injuries,” Symons said.
“Marcus is looking more severe at the moment but until we get a scan and see a specialist we won’t know. But it’s looking quite nasty.”
The injuries compounded a miserable night at the KC Stadium for Fulham, who lost 2-1 and now just have one point from their opening three Championship matches.
For the third game in a row, shipping a late goal proved to be the London side’s undoing – with Sone Aluko coolly slotting home from Jelavic’s knockdown after former Hull midfielder Tom Cairney looked to have claimed a point for Fulham.
“It’s only three games in and I’m sick of saying the same things already,” Symons added. “Late goals are costing us dearly.
“Our fitness levels are very, very good. We’re generally higher level second half than we were first half. It can’t be down to fitness, it must just be down to concentration, not being street-wise enough. It’s costing us dearly and it needs to change.”