I really think that Salah starting is mandatory. It is true that at times he might have looked a bit rusty or leggy, but that's only in comparison to the image we now have of the immense player he proved to be last season. If I remember correctly, after the first few games this time last year, people more often than not failed to see a world-class player in him--but gradually he became an untouchable asset of our team. Time will tell. It did last season, and in what a great manner.
I recall that in the game vs City, at the Etihad last season, when we lost 5 to 0, Salah missed a good chance when we were 1 down, and the commentator hastened to state that Salah is ''no Aguero''. So--at the beginning of the season we was looked upon as a lesser player compared to Aguero, and behold how that turned over!
I think it is obvious from his game that he remains, his ephemeral form notwithstanding, an incredibly dangerous player--the way he attacks the ball, the way he attacks the open spaces, the channels behind players (which, make no mistake, now are more prepared to deal with Salah, having studied him beforehand, unlike last season, which does nothing but add to the difficulties our player faces in his quest to replicate his blazing performance from last campaign), his positioning in attack when receiving the ball, the pressing, the tracking back when defending, his presence around the opposition's box, his touches (not quite as sharp as we would expect of him, but still irrefutably classy), his turns, his movement from right to left etc. all contribute to asserting that Salah is a phenomenal player, and I have no doubt that he will find his form sooner rather than later.
Having said these, I maintain that we absolutely have to start him tomorrow, and next week against Chelsea in the league, because he is, quite simply, one of our best players.
And one more thing, just remember from last season how impotent our team looked at times when Salah went off or missed from our game. When he was subbed against City at home in the UCL, or against Roma, or, sadly, against Real Madrid--he has an aura about him that no one can deny: he possesses a fear-inducing factor that few players do; when he has the ball, you just expect things to happen and can observe how the opposition's defense start panicking, because they know he can change a game on his own. He has to start most of our games.