Manchester United have confirmed midfielder Kobbie Mainoo will be out for a "few weeks" with a muscle injury.The England international suffered the problem during United's 0-0 draw with Aston Villa before the international break, which he was subsequently ruled out of.United have now revealed he will be out number of weeks, along with Harry Maguire, who picked up an injury in the same game.However, Noussair Mazraoui returned to training on Thursday following his recent medical procedure after suffering heart palpitations.The Morocco international underwent a precautionary, minor corrective procedure to rectify a relatively common condition last week.He returned to training at United’s Carrington training ground, but this was the first step of his recovery and it is not yet known he whether he will be fit for Saturday’s Premier League visit of Brentford.Alejandro Garnacho (knee) and Amad Diallo (illness) were also back after missing games for Argentina and Ivory Coast respectively, and look set to be involved against the Bees.Brentford boss Thomas Frank feels Erik ten Hag is facing "too much" criticism after a disappointing start to the season that has piled pressure on his Manchester United counterpart.The Dane, who celebrates six years at the Bees helm this week, is himself one of the names linked to United should the Dutchman depart.Frank's men travel to Old Trafford on Saturday lying 11th in the Premier League with 10 points, two clear of Ten Hag’s 14th-placed side."It’s incredible how much scrutiny he’s had to face," Frank told the Brentford website."As a head coach, I acknowledge how it feels to be in a situation like this.