Just as you think Manchester United have turned a corner this season, they return to square one.Ole Gunnar Solskjaer's side have enjoyed big wins over Spurs and Manchester City this month in the Premier League, whilst they have also advanced into the Europa League last 32 and the semi-finals of the Carabao Cup.But it hasn't been the matches against the top sides that has been the issue for United this season. Instead, they have struggled against teams below them who sit back against them and don't let them counter-attack.And this trend continued on Sunday afternoon, with United falling to a woeful 2-0 defeat to rock-bottom Watford at Vicarage Road to add to disappointing losses to the likes of Bournemouth, Newcastle and West Ham this season.After a dull first half, the game was sparked to life when David de Gea inexplicably let Ismaila Sarr's bouncing shot squeeze through his hands, and from there, Watford never looked back.David de Gea makes an absolute howler in Watford vs Manchester UnitedGary Neville's brilliant reaction to David de Gea's howler in Watford vs Manchester UnitedJesse Lingard has gone exactly one year without scoring a Premier League goalFor once, Aaron Wan-Bissaka mistimed a challenge in the box to let Troy Deeney double their lead from the spot and United couldn't find a way back into the game.The spotlight will be firmly on de Gea however, after another high-profile mistake from a keeper that has seen his form drop off dramatically in the last couple of seasons, having been so impressive previously.The Spaniard had established himself as arguably the best goalkeeper in the world a few years into his career at Old Trafford, but his current form is seeing him fall behind the likes of Alisson, Ederson and Marc-André ter Stegen in that list now.And a stat that Opta tweeted today only reinforces that thinking.

An incredible stat really considering how good we all know he is.

You can't doubt how good he is at reflex saves but what the stat does suggest is that his concentration might be the issue, particularly when United are struggling so much in games where they dominate possession and he isn't worked as much.

There's no doubt that United fans will be subjected to more days of frustration in the near future as they continue their period of transition that doesn't seem to have an end in sight.

But if they are to drag themselves out of the mire that they find themselves in, they'll need de Gea to rediscover his best form sooner rather than later.