Chelsea midfielder Michael Ballack is to undergo further surgery on his ankle after developing problems following an initial operation in May.

A statement on Chelsea’s website said: “The operation is related only to a complication in the healing of the wound from previous surgery.”

Ballack, 30, could miss the club’s tour of America which starts on 10 July.

Ballack first injured his ankle in a game against Newcastle on 22 April.

He has not played since and missed Chelsea’s win over Manchester United in the FA Cup final and both of Germany’s Euro 2008 qualifiers in June.