That's really surprising thing to hear and same here this is the first time I am hearing a professional player that plays actively in Europe failing medical test. I don't know if Boniface is to be blame in this situation but I think it's regarding an injury on his knee but I am not too sure.
Some Nigerian fans have been criticizing him on social media for not taking is career too seriously and that is why his move didn't go through and as it stands now I don't think any team would want to sign him with the injury. I just hope if he goes back he will be missed by Ten Hag else he would have to wait another transfer window.
This certainly not the first case of an European player in as much as this is a very rare case and not common there have been cases of these in the past, I can still remember when Hakim Ziyech move from Chelsea to Al Nassr collapsed due to failed medical with the player having an untreated knee. Then there is this Nabil Fekir failed transfer to Liverpool then when the player was at Lyon and it was reported that it was this same Knee injury. Even this season Boniface fellow Nigerian player and AC Milan forward Noah Okafor had his deal collapsed while moving to Leipzig after failing Medicals and he is currently at leads united. So there have been many cases but must of the time it is usually when there is a knee injury which we all know is a serious injury to treat and still remain fit for a long time.
You talk as if he chose Manchester United... But no, initially there was only talk of Manchester City. As for Manchester United, their problems as a club, which is currently in poor form, were discussed. And besides, Donaruma's transfer hasn't been finalized yet, if it's going to happen at all, because time is running out and there's no news.
Manchester United only inquired about him when the club noticed that they were issues between him and PSG but they later saw that the deal was far beyond them because Donnarumma will only be coming to a club without champions league football for high wages and it’s the reason why Manchester United didn’t push more again. They are currently closing in on Semenns from Antwerp
In fact, if they had continued to fight, who knows, maybe the player would have agreed. The chances were slim, but they existed, and Donnarumma would definitely have helped them. Nevertheless, he is now negotiating with Manchester City, but everything depends on whether they can keep Ederson, and if so, Donnarumma will not be needed even at Manchester City. Surprisingly, he may end up without a club.