The Belgium international has not travelled with the squad to their Dubai training camp but instead visited a doctor in his homeland for treatment on a calf problem.
"We know that for 10 days Rom has had some problems with his calf," Koeman told evertontv.
"He has a lot of confidence in the Belgian doctor and I gave him permission to go to Belgium and recover.
"We expect him, normally, next Tuesday to be joining in the training session. He will be fit and available for the weekend."