If - and this is way off in the future, so anything written now is entirely speculative - we end up working out our divorce from the EU in such a way that we don't grant any concessions of freedom of movement whatsoever (which I would think is unlikely, but as I say that is my speculative opinion rather than anything concrete), then the biggest possible sea change for football would be that the rules applying to work permits that are in place currently for non-EU players would be extended to all players without a UK passport. So they'd need to play for a team in FIFA's top 70 (I think) and have played 75% of the games for the national team over the last two years, subject to availability with special circumstances sometimes applying. But this would be unlikely to apply to any players currently playing in Britain or who have been here for a significant length of time, as Nouha has.
At present the FA cannot introduce their own laws saying that a certain percentage of the squad must be English/British qualified because it contravenes EU law. That might well change in the next 4-5 years depending on the political landscape. So there is the possibility that in say, 2020, there are rules in the Football League that say you must have, for example, a minimum of 15 British players in the matchday squad. There is the possibility that clubs will no longer be able to sign relative journeymen from Europe as they won't be granted a work permit. But that's all a long way off and anything could happen.
I doubt anything will happen in the Premier League, they cannot peg themselves as one of the top leagues in Europe if they have strict restrictions on the number of foreign nationals, because it just means they'll get hoovered up by clubs in Spain/Germany/Italy instead and our teams' performance in European competition will inevitably suffer in comparison.