Lennox Lewis was threatened with legal action on Tuesday after pursuing a re-match with Mike Tyson instead of a scheduled fight with Ukrainian Vitali Klitschko.

World heavyweight champion Lewis, 37, had been due to fight Germany-based challenger Klitschko in April.

But Judd Burnstein, Lewis' attorney, revealed on Monday that the Briton would return to the ring on 21 June, depending on how Tyson fared against Clifford Etienne next month.

"I must clearly say that I regard this as a breach of contract," Klitschko's promoter Klaus-Peter Kohl said.

"I will hold talks over the next few days and study all options regarding possible legal action."

Klitschko's management company, Universum Box-Promotion, said they had signed a contract last December for a Lewis-Klitschko fight to take place either on 12 April in Las Vegas or on 19 April in New York.

"Lewis has the obligation under the World Boxing Council rules to take on Vitali in his next fight and we will not wait any longer," Universum executive Peter Hanraths said on Tuesday.

"Either Lewis does that or the WBC must strip him of his title."

Lewis comprehensively defeated former undisputed world champion Tyson in eight rounds last June.