From my understanding he can't play football again in the sense that he can't 'play' play, at the level he aspired to be. Per Ch1 etc he was a bit of a prodigy winning MVPs at prefecture level and being scouted by clubs, he could have went on to play pro in front of thousands of people and make a living out of it. After doing his knee he's lost two critical years of development and might never be good enough again to play at a professional level, though he's now well enough to play recreationally. Naoki is like 'I think you look happiest playing football, I know you probably can't go pro anymore but why don't you go play with the school football team 4fun?'See I'm confused, I thought the nature of his injury meant that he could never play soccer again. So idk why she's suggesting for him to join the soccer team.