Reckon there's about a dozen, but there's so many reasons why nobody will make it public any time soon.
There's still large parts of the world deeply opposed to homosexuality. If you're a gay footballer playing you're going to have issues when playing any away game, especially in Europe or international football. There will be taunts from your own fans every time you makes a mistake, every time you're spotted in public etc. Just look at all the abuse Bellerin got the other day.
I've heard countless stories about friends/family rejecting someone who comes out as gay. In a Premier League dressing room you're going to have 40-50 people once the squad players, coaches, support staff etc are factored in. Not all of them will be your friend, and someone is bound to take issue with it.
I don't think I need to explain to anyone how the gutter press would respond to it either. The star players at Liverpool, Arsenal, United etc are used to constant press attention and negativity, but would the back up at Cardiff City be able to handle it?