Ghana's Michael Essien is a doubt for Tuesday's must-win clash with Burkina Faso, after picking up a fresh injury.The Chelsea midfielder hobbled off the Black Stars' team bus after training with an injury to his right knee.Officials confirmed it is a different injury to the hamstring problem that prevented him from starting Friday's 3-1 defeat against Ivory Coast."I don't know the extent of the injury but we will find out later," Ghana coach Milovan Rajevac told BBC Sport.Shortly before 1500 local time on Sunday, the 27-year-old was taken to hospital in an ambulance as he went for tests to determine the severity of the injury.Essien, who played 45 minutes as a second-half substitute in the Group B clash in Cabinda, trained on Sunday morning but had to come off early.He had only returned to training with Chelsea on 6 January after nearly a month out, having not played since suffering a hamstring injury on 8 December.If Ghana fail to beat the Burkinabe on Tuesday, the World Cup finalists will exit the Nations Cup.Ivory Coast have already qualified from Group B, with four points from two games, while Burkina Faso have one point and Ghana none.After Togo's withdrawal from the competition following the gun attack on their bus, Group B was reduced to three teams and just three matches.Source: BBC