Cuper opted not to use Salah for Egypt's Group A opener and the Egyptian Football Association subsequently released a statement indicating the attacker could have played, at odds with the assessment of the coach.
As for Egypt, a first win at a World Cup at the seventh attempt is the aim when it plays Saudi Arabia in Volgograd on the same day.
Remarkably, it was the fifth own goal of the tournament so far.
The tournament hosts came away with a 3-1 win in St Petersburg.
But after Fathi put into his own net, an inspired Cheryshev slotted in his third goal of the tournament, putting him equal with Cristiano Ronaldo in the top scorers' chart.
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Our fans have been hugely supportive and this has been much appreciated during a challenging but momentous time. After the opening-weekend game at Etihad Stadium, the Gunners travel to fellow top-six contenders Chelsea .
"Salah is fit. In the previous match against Uruguay we thought he was fit also but we always draw up a last physical test", the former Valencia boss explained. Even then, they would need a higher goal differential than Saudi Arabia and Uruguay to qualify as second in the group.
"Every company has the right to sponsor stars to travel, but why are they all staying so close to a team that is supposed to be in a state of focus and readiness?" tweeted famous Egyptian sports expert Yasser Ayoub. The record amount for a World Cup is six in 1998.
Shinji Kagawa scored from the penalty spot and although Juan Quintero equalised late in the first half, Japan made their superior numbers count, with Yuya Osako heading a victor in the 73rd minute.
Certainly, he was not 100% fit, that much had been clear on Monday when Salah jogged around the Saint Petersburg Stadium pitch, testing out his left shoulder with a series of tentative barges but opting out when his team-mates swung their arms in circles.
"Today we'll have an important test for him to see how he does". Tunisia lost 2-1 to England on Wednesday after an injury time header from Harry Kane.
The 26-year-old made his first appearance since being withdrawn as Liverpool were beaten 3-1 by Real Madrid in the showpiece fixture of Europe's premier cup competition, claiming a place in Hector Cuper's starting line-up.