Chelsea's Michael Essien could miss the World Cup with Ghana after struggling to overcome a knee injury.Essien, 27, hoped to return against Stoke on Sunday but looks unlikely to play again this season and says his World Cup campaign could be in doubt. [LNB]He said: "I'm taking it day by day and if I can make it I will." [LNB]Chelsea also look set to finish the season without John Mikel Obi after the midfielder tore his meniscus in the 2-1 defeat against Tottenham on Saturday. [LNB]Mikel left the pitch at White Hart Lane after just over half an hour and told KickOffNigeria.com that he had a tear in his knee. [LNB]He said: "I won't play this weekend and the doctors say it will take about three weeks to heal, although there will be no surgery." [LNB]Mikel has been named in Nigeria's World Cup squad of 44 and says he intends to be at their training camp in England at the end of April. [LNB]"It is very important for all of us as players to get together, even if there is no match," he said. [LNB]The loss of Mikel will come as a blow to Chelsea manager Carlo Ancelotti, who has been without Essien since he tore his hamstring against Apoel Nicosia in the Champions League in December.[LNB] Can Chelsea cope without Mikel and Essien? Essien then hurt his knee on international duty at the Africa Cup of Nations in Angola in January but had only been expected to be out for six weeks. [LNB]It was anticipated that he would make his comeback for Chelsea for the visit of Inter Milan in the second leg of their Champions League tie on 16 March. [LNB]But the midfielder's knee continued to swell up and the player underwent four lots of surgery inside a fortnight. [LNB]Essien is central to Ghana's hopes in South Africa, but with their first game against Serbia on 13 June, he is reluctant to play unless fully fit. [LNB]"The World Cup is the best and most difficult football tournament in the world and I would rather be there fully fit," he said on his official website. [LNB]"We will just have to wait and see. If not I'll have to sit at home and support the team like every Ghanaian." [LNB]Chelsea have Stoke, Liverpool and Wigan still to play in the league this season, and Portsmouth in the FA Cup final at Wembley, but Essien and Mikel could now miss them all. [LNB]A Chelsea spokesman said: "The Ghanaian's participation in the remainder of the campaign is in doubt."