Salah, who celebrates his 26th birthday today, has been nursing a shoulder injury from the UEFA Champions League final defeat to Real Madrid last month.
However, the Liverpool forward has worked tirelessly with the Pharoes medical staff and during training sessions by himself in order to feature against the South American - who are favorites to top Group A.
"Salah is doing very well indeed, he's recovered very quickly. We'll see how it goes today. I can almost assure you 100 percent he'll play," Cuper said in the pre-match press conference.
"We're trying to make him feel confident. The doctors are giving him the option to play or not. I know him very well, and I'm sure he’s not afraid.
"A risk of playing a match is something we can't hide. In terms of him on the pitch, he'll have full guarantees. If we do see at the last minute there’s an issue, we'll see if it can be resolved."
Cuper went onto tip the forward to lead the seven-time African champions to replicate his club form, which saw him net a staggering 44 goals this season.
"He could be the top scorer and one of the greatest players," he exclaimed.
"He's shown he's got great personality, talent and character. No-one thinks he can’t [be top scorer].
"We'll see great players here and he can be the greatest player [of all] at this World Cup."