Premier League Golden Boot winner Salah suffered a shoulder injury after tangling with Madrid captain Ramos in the Champions League final last month, sending shockwaves through Egypt heading into the World Cup.
Preparing for the showpiece tournament in Russia, Spain defender Ramos claimed Salah could have played on if he had an injection as Madrid emerged 3-1 victors in Kiev , while he sarcastically mocked the Reds for making excuses.
However, Cuper believes Salah would have wanted to stay on the pitch if he was able to as Madrid claimed a third successive title.
"I'm not a doctor, I don't know if [Sergio] Ramos is a doctor, but it's a player who is playing a final and has an injury," Cuper told reporters prior to Wednesday's friendly with Belgium.
"I don't have any doubt that if he could keep playing he would do it, because a Champions League final is extraordinary."
"My opinion is that Salah has an important injury, there is a recovering [process] that we can see, and we are optimistic about the chances he has to play in the World Cup," he said.
"We listen to many things, but the reality is that the doctors recover or confirm a problem in a player."