Cristiano Ronaldo was forced to leave Manchester United training early on Thursday after picking up an injury. The Portugal international had been dealing with a hip problem in the build-up to Monday's FA Cup victory over Aston Villa which saw him left out of the squad, although the injury was not believed to be serious. According to The Sun, he was soon back in training after shaking off that issue but has since picked up a new knock which left him unable to complete the session on Thursday. Club doctors looked at Ronaldo before sending him home early, and his involvement in Saturday's Premier League clash with Villa now looks to be in doubt. The legendary forward recently discussed his frustration towards United's struggles in the league, admitting he will not be happy until he sees the Red Devils reach the top three at the very least, but there are now concerns that he will not be back in time to help out this weekend. The 36-year-old is desperate to return and has spent time in the oxygen chamber in his house to try and accelerate his recovery. With Ronaldo unavailable for the cup clash with Villa earlier this week, manager Ralf Rangnick opted to shift from his favoured 4-2-2-2 formation and instead went for a 4-2-3-1 with Edinson Cavani up top alone. He could stick to that for the league meeting between the two sides on Saturday or opt to play Mason Greenwood in his natural position alongside Cavani in attack.