The 19-year-old, who is on a season-long loan at The Hawthorns from Chelsea, was placed on the sidelines for national side Belgium due to an ongoing ankle problem.
"We're hopeful Lukaku will be fit," Clarke told the club's official website. "He's had a pain in his ankle for a few weeks.
"He felt it again when he came off the bench against QPR and didn't feel it was right to go. He went across and got it assessed by the Belgium doctor and got sent back. It's not a big problem but it's one we're mindful we don't want to become a big problem. We're monitoring it."
Clarke has also confirmed that Jerome Thomas is nearing a return to action after a knee operation.