<text>  Antonio Valencia has apologised to Manchester Uniteds players and fans after his mistakes helped Arsenal dump his side out of the FA Cup in Mondays quarter-final defeat. The cup exit effectively ended any hopes of silverware ended up at Old Trafford this season - and Valencia more than played his part in a dismal display from Louis van Gaals side. The midfielder-cum-defender put in a weak challenge and allowed Alex Oxlade-Chamberlain to set up Nacho Monreal for Arsenals first before playing a poor backpass to set up Danny Welbeck for his second-half winner. Antonio Valencia was poor for Manchester United on Monday night and was at fault for two goals . The midfielder-cum-defender inexplicably let Danny Welbeck in for the winner with an awful backpass . Nacho Monreal left scored Arsenals first, with Valencia involved in the defensive collpase . Valencia posted this lengthy apologies to his team-mates and supporters after the defeat by Arsenal . Valencia was panned by fans and television pundits alike for his awful performance, and the 29-year-old has now offered up an apology for his showing. I want to apologise to my team-mates and the fans of Manchester United, Valencia said on Instagram. Tomorrow is another day and keep working, he added before tagging team-mates Marcos Rojo, Juan Mata, Ander Herrera, Rafael and Robin van Persie in the message. Valencia tries to get close to Chile winger Alexis Sanchez during Monday nights FA Cup defeat . Former United captain Roy Keane called Valencias defensive contribution disgraceful and accused the Ecuadorian of downing tools in his television analysis. And things got even worse for Van Gaals first choice at right back on Tuesday when Rafael put in a brilliant - and goalscoring - performance for Uniteds Under 21s to pile the pressure on Valencia ahead of Sundays Barclays Premier League clash with Tottenham Hotspur. Rafael left was excellent for Uniteds Under 21s, scoring and looking a viable alternative to Valencia . 