Speaking after his side's friendly draw, Cuper said he still remained confident Salah would be fit for the showpiece tournament.
"We are optimistic, and every medical report says he will make it," he said.
"But we still have to prepare for any situation that could happen before we start."
Cuper said his side missed Salah, while adding Ramadan had impacted his players' energy levels.
"Salah is not easy to replace, no doubt about that," he said.
"He is a weapon for us, especially on counter-attack, making use of his speed and his quality.
"That's why today we struggled in our attacking performance. We tried to compensate that with some team playing, but as I said in the second half we lacked stamina because we have a special condition … for religious reasons, players don't drink nor eat anything, and we actually felt that.
"We tried to manage it using the whole team so it could try to respond better. We sprinted very well, because it was not easy to recover the ball."
The Egyptian FA have previously announced that Salah's absence will "not exceed three weeks", which puts him in contention to play some part in the group stage for the Pharaohs.