When Salah is playing like that, the only left back that's handling him is also wearing a Liverpool shirt. From what I've watched of City, Cancelo is more of a midfielder in position and against a team that can break as quickly and effective as Liverpool, it's going to be an issue. Having a real fullback like Walker but on the left is obviously something that is missing in those big big games where the opposition have top class all over.
Today, albeit interesting, doesn't really change anything. Cancelo is still a top class player and in any game against a team without top attackers, he will shine as usual. Potter probably lied about the injury because saying "we left him out cos he might go city" isn't very good, his replacement Webster was great (friendly etc but still) and no doubt Brighton have someone in mind to bring in, hope this can get done relatively soon so that everyone can be happy and move on.