Chelsea's Michael Essien may sacrifice playing for Ghana at the World Cup for the sake of the rest of his career.Essien, 27, has not played for Chelsea since tearing a hamstring in December. He then hurt his knee on Ghana duty at the Africa Cup of Nations in January. [LNB]"If I make it for the World Cup then great - if not I have my whole career ahead of me," he told Chelsea's official website. [LNB]"The last thing I want is to rush back and cause more problems down the line." [LNB]Essien's last run-out in a Chelsea shirt was against Apoel Nicosia in the Champions League in December. [LNB]Having recovered from his hamstring tear, he then hurt his knee at the Africa Cup of Nations, but that was only expected to keep him out for six weeks.[LNB] PIERS EDWARDS BLOG Essien's absence would be a hammer blow to Ghana's hopes - 'indispensable' is what one former national coach calls him It was anticipated he would make his Chelsea comeback in the Champions League game against Inter Milan, but his knee continued to swell up and he 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 has admitted that he might be forced to look on as a spectator. [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 could also be without John Mikel Obi for their remaining fixtures - against Stoke, Liverpool and Wiganin the league and Portsmouth in the FA Cup final. [LNB]Mikel tore his meniscus in the 2-1 defeat against Tottenham last Saturday, telling KickOffNigeria.com: "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.