Liverpool's Salah sat out the 1-0 loss to Uruguay after injuring his shoulder in last month's Champions League final.
Russia's 5-0 win against Saudi Arabia was the biggest victory by a host nation in an opening game since Italy beat the US 7-1 in 1934.
Cuper's team showed against Uruguay they will not defend as generously as the hapless Saudis, and Salah, who should make his first start, will relish the chance to torment Russia's aging defense.
The tricky striker stayed on the bench in Egypt's 1-0 defeat to Uruguay.
Hosts Russia moved closer to qualification for the next round of the 2018 World Cup courtesy of a comfortable 3-1 victory over Egypt in Group A at the Krestovsky Stadium this evening.More news: M’Baye Niang pounces to secure Senegal victory after Poland mix-up
Left-back Yuri Zhirkov trained individually on Sunday because of a minor ankle problem but is likely to be passed fit. Three goals came from reserves, and two of those came from Denis Cheryshev, a talented winger at Villarreal and former youth player for Real Madrid.
In the end, however, the response was unable to conjure any sort of comeback for the Egyptians, as Stanislav Cherchesov's charges eased to an emphatic win that now leaves the hosts on the verge of reaching the knockout stages.
The Egyptian Football Federation (EFA) laid that decision exclusively at Cuper's door, maintaining the 26-year-old was fit to face Uruguay but deemed not ready for the risk.
On the other hand, Russian Federation will be without Alan Dzagoev after the 28-year-old was injured against Saudi Arabia and will miss his side's games against Egypt and Uruguay.
If Egypt are to get a positive result, they will have to stop midfielder Golovin from getting the ball in space.
The 26-year-old will be full of confidence following a stunning debut campaign at Anfield that saw him score 44 goals and scoop the PFA Player of the Year award.More news: FIFA 2018: Russia sour Salah's return to close in on last 16
On the other hand, Egypt's majority of goals were from cross balls, so Russia's weakness plays particularly well in Egypt's favor.
Egypt's first World Cup since 1990 did not get off to the best of starts.
Finally, Mourinho concluded that Russia's match against Egypt is crucial as the Uruguay match is a hard one, "The game against Egypt is the crucial match of the group".
While Russia coasted home with a 5-0 margin against Saudi Arabia, Egypt will provide a much tougher test.
Egyptian players circled Argentine referee Enrique Caceres arguing a push on Fathi but the goal stood to their dismay.More news: Barty faces Konta in Nottingham final