I can't recall who, where or what, but I remember a player coming back from the African Cup of Nations a few years back to the Premier League due to "injury", and then appearing in a match day squad as the ACN was still ongoing. That is shitty, and if the Joel Matip saga was anything along those lines, I'd completely agree with the Cameroon FA.
However;
It isn't. He hasn't played for them since 2015 and wasn't selected to be in their final squad. Does that mean any Cameroonian international, not currently with the national squad is banned from playing for their respective clubs?
We should play him against Plymouth, no doubt. FIFA haven't got a clue, and what kind of precedent does it set if Matip has to sit it out until Cameroon are knocked out in future? Every time they have a match and Matip isn't included, does he have to sit it out? Nah, play him and show FIFA and the Cameroon FA they can't hold Liverpool and Joel Matip hostage.