The Cameroonian completely misjudged what looked like a simple save from Morgan Gibbs-White's shot as the hosts suffered a hugely disappointing defeat
Ruben Amorim was reminded of the gravity of the task facing him at Manchester United as his side sank to a second successive Premier League defeat on Saturday, losing 3-2 at home to Nottingham Forest.
United got off to an awful start when Nikola Milenkovic out-jumped Lisandro Martinez to head home from a corner in just the second minute. It was the third goal the Red Devils had conceded from a set-piece in two games after being bombarded by Arsenal. Rasmus Hojlund equalised on the rebound after good play from Manuel Ugarte and United nearly went ahead before the break when Bruno Fernandes smashes against the bar from a free-kick.
But United made another terrible start after the break as Morgan Gibbs-White restored Forest's lead after feeble goalkeeping from Onana, who was culpable once again when Chris Wood made it 3-1.
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A ferocious strike from Fernandes gave United hope of a comeback but they rarely looked like equalising.
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