The Highlander was due to face Sexton for the vacant belt at Ravenscraig Sports Centre in Motherwell on Saturday (May 20).
But the show – also due to feature Connor Law, Eddie Doyle, Rhys Pagan, JP McGuiness, Leon Roberts and Martin Taylor- has now been cancelled after ex-Commonwealth champ Sexton called off.
Promoter Paul Graham – who won purse bids to stage the contest – said: “I’m absolutely gutted for Gary because he had a real chance of becoming Scotland’s first-ever British heavyweight champion – and on home soil too.
“But we’ve been left with no choice other than to cancel the show because Sexton has pulled out.
“His manager hasn’t spoken to me, but he called the British Boxing Board of Control to say that Sexton has had to withdraw on medical advice.
“I don’t yet know what that means and whether it’s injury or illness which has forced him out, but I’m sure I’ll find out in due course when he supplies his medical certificate.
“We’ll await confirmation that Sexton is back in training in due course and hopefully look to reschedule early next season, in September or October.
“It’s a real disappointment for all the other boxers on the bill and Scottish fans in general, but it’s just too late draft in a replacement to face Gary in a fight of this magnitude.”