There is absolutely ZERO chance that Pogba could fly to Manchester on a commercial flight and not have twitter blow up with reports of it. It's one thing for him to get minimal attention flying from Vegas to New York, but flying to Manchester, at least half the plane would know who he is and why he's headed there, not to mention all the people that would see him at the airport after departing the plane.
IF he has flown to Manchester, it had to be a private jet. He posted something on Instagram at 3 or 4am NY time, so while he could have had insomnia, there's certainly a decent chance that he was awake for some other reason (such as being on a plane or arriving in a timezone 5 hours ahead of New York). Hypothetically, if he arrived in England before 7 or 8am, he could probably easily go unseen except by very few, especially if he's flying private.
In fact, if he hasn't already flown in, I'd guess that it will be private to avoid all the attention that him boarding a flight to England would generate.