Kind of does work like that though, because he's only available half the time you have to buy and pay someone else to play the other half of his games.
That might have been true 30+ years ago with smaller squads but I disagree that you HAVE to buy and pay extra players. You may or may not choose to do that but these top clubs have big squads, in fact so big they sometimes can't even register all their players in a 25 man squad. Liverpool don't have Salah, Mane, Firmino, Jota and Diaz all in the starting XI.
Effectively this argument would infer that if Liverpool bought Dembele then probably the 'effective' wage of Diaz/Firmino/Jota or whatever goes up because they will play less games due to Dembele stealing games off them. I just don't like it. It's the overall total squad wage that really matters.
Of course it works like that. If I went for a job on £100k/year full time and then said "oh yeah, by the way I am only going to work 2 days a week" they probably would want to reduce my wages or tell me to **** off.
If you have a long term injury record that suggests you only play half of the games then any wage discussions will obviously take that into account. Its not going to be 50% of the salary for 50% of the games but it might only be 60-70% of the salary they would offer if you have a good injury record. Perhaps it will be more heavily "game time" weighted.
Most players who are getting injured a lot don't suddenly get injured less as well. PL is a hard league vs Spain as well.
By this logic nearly all players have bigger salaries then because except keepers very few players play every match.
The analogy just doesn't wash with me because this isn't Dembele telling a club he will only play half the games. It's down to the club to structure a mutually agreeable contract offer, if they think he's injury prone or whatever then they adjust accordingly
Often it's the club that decides a player isn't playing a given match, not them.
Like you say if you have concerns about injuries then you structure the contract to suit, appearances bonuses and suchlike. You don't just go "ok we pay him £300k/week but book that as £600k/week because we expect him to miss half the games".
You only have to pay players their salary. If a player is on £300k/week (£15m/year) and plays one game a year out of say 50 you don't have to pay them £750m/year. The actual money changing hands doesn't change so it's not something that directly impacts the finances. So a player doesn't "cost a small fortune in wages" just because they have historically played fewer games. You could consider them not good value but it doesn't actually mean paying them more money.
I do understand if you have an entire squad full of sicknotes you would need more players and hence indirectly have increased costs but that still doesn't mean the player in question is actually getting any more money and these things are balanced out over big squads anyway. Like I say, it's exceedingly rare for an outfield player to play every single match anyway.
You also have insurance to cover injuries and potentially other scenarios that mean players can't play.
Don't want to get into a debate about Mane vs Dembele but if people are rolling out all these stats don't forget Dembele actually has a better ratio of goal involvements (goals plus assists) to appearances than Mane in league matches this season.