The American midfielder took a blow to his knee in the 3-0 defeat on Wednesday and was replaced by half-time by loanee Vladimir Weiss.
Full-back Sasa Papac also picked up a gash to his head, but Smith insists his injury was far more straightforward.
"Sasa Papac is fairly straightforward, he has 10 stitches above his eye," he continued.
"We don't know how bad Edu is. He has taken a knock on the knee but how bad it is we won't know for maybe a day or two."