The striker sustained the problem in a friendly against Stoke on Tuesday, leaving the Britannia Stadium on crutches.
Despite the Wales international not requiring an X-ray, the bruising to the bone makes him a doubt for Tuesday's visit of Middlesbrough.
"He has got a sore foot but it's nothing too drastic," Clarets manager Sean Dyche confirmed on the club's official website.
"It was studs across the foot but we are hoping that settles down quickly.
"It is sore but we can only be hopeful that he is available for Tuesday."
Meanwhile, Ben Mee is close to a return to full training after a knee injury that has kept him on the sidelines since December.