Billy Doctrove, the joint umpire in the forfeited England-Pakistan 2006 Test, failed to show up to Darrell Hair's employment tribunal on Thursday.
Doctrove and Hair officiated the controversial Oval Test in 2006
Doctrove, a key witness for Hair, had been due to take the stand but did not board a plane from Dominica to London.
Hair's representative Stephen Whale said Doctrove's absence was because of "reasons too confidential to explain".
Hair, who was sacked from Tests by the International Cricket Council after the game, is claiming race discrimination.
The 55-year-old will argue that while he, a white Australian, has been severely punished his co-umpire Mr Doctrove, a black West Indian, has escaped all censure.
However, explaining Doctrove's failure to attend the hearing, Whale said: "He told the instructing solicitor he was not getting on the plane. This is for personal reasons that are too confidential to explain.
"As a matter of formality the claimant is not saying that Mr Doctrove will not be coming to this hearing, just that he will not be coming today."
Both umpires - Mr Hair and Mr Doctrove - penalised Pakistan for ball tampering and then awarded the match to England when the tourists refused to continue in protest at the notorious Oval Test in August 2006.