The Welshman was due to face former world champion Jonathan Barros on the undercard of Carl Frampton’s clash with Leo Santa Cruz in Las Vegas.
But Argentine Barros failed to meet the Nevada State Athletic Commission’s medical requirements.
Selby said: “I’m almost in tears. This was my big chance to shine but I promise I will be back here.”
The Barry-born boxer was ready to weigh in when he was informed of the news.
Lee Selby's fight with Jonathan Barros has been cancelled
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Carl Frampton will take on Leo Santa Cruz in Las Vegas
Barros failed to turn up to yesterday’s final press conference because he was dealing with the medical issue.
But Nevada officials refused to allow him to box and Selby has been left frustrated.
The Welshman was hoping an impressive performance would also secure a summer showdown with Frampton if both men came out on top this weekend.
He added: “Hopefully I can get a fight sorted and a quick win under my belt so I can fight the winner of that fight.”