The 22-year-old had hoped to be fit for the April 16 date at Wembley after sustaining the injury on England Under-21 duty last week - but he is expected to be out of action for between four and six weeks. Richards told the club's website: "It is not what I wanted to hear at all. I felt sick when I was told. I knew from experience when I did it that it felt like a bad one but I was hoping for the best. "All I can do now is concentrate on getting back as quickly as possible. I must admit I did think 'why me?' for a while when I heard the news. "Of all the games to miss, a Wembley date with United is the last one any player would choose." Despite the prognosis, Richards has not given up hope yet and is proceeding with plans to install an oxygen tent in his house to speed up his recovery. City, meanwhile, are hoping fellow full-back Jerome Boateng will not need knee surgery after he also picked up a serious injury on international duty. Initial reports from the German camp suggested the 22-year-old would have to go under the knife but City are seeking a second opinion from the club's medical staff. The double blow has left Roberto Mancini short of defenders for Sunday's clash against Sunderland at Eastlands, with Pablo Zabaleta still on compassionate leave in Argentina and Kolo Toure suspended, meaning youngsters Dedryck Boyata and Reece Wabara could come into contention. A first Premier League appearance for centre-back Wabara would be the perfect way for the 19-year-old to celebrate his new contract. The Academy graduate on Tuesday penned a new three-year deal having featured in the first-team squad on a number of occasions in recent weeks. Wabara said: "I've been working really hard to improve all areas of my game so I'm delighted to have signed this new deal. "It was a big relief to know one of the most ambitious - and soon to be biggest - clubs in the world wants me to be part of their future. "I don't know whether I'll be involved against Sunderland or not yet so I just need to work hard and be prepared if and when I'm needed."
