What size should I get of a jersey for my boyfriend?

I want to get a football jersey for my boyfriend but I genuinely have absolutely no clue on what size to get 🥲 he's quite tall, a bit more than 180cm and i think he's closer to the slimmer side even though he does work out. Im considering a M which has chest size as 38 inches and L which has chest size 40. I don't want it to be too tight or else he won't be able to play football in it, so im thinking I should maybe go for the larger size to be sure? But what if the larger size isn't big enough? 😭 I can't ask him because he'll obviously catch on so i genuinely don't know what to do rip please help