Australia duo David Warner and Marcus Stoinis have withdrawn from this summer's men's Hundred competition.
The pair were due to play for Southern Brave but have pulled out because of coronavirus restrictions.
They are both also named in Australia's squad for tours of the West Indies and Bangladesh in July and August.
"It is obviously disappointing to lose players with the ability of David and Marcus," an England and Wales Cricket Board (ECB) spokesperson said.
"But the realities of Covid means there are practicalities that are difficult for some overseas players to overcome.
"Replacement overseas players will be signed by Southern Brave, and we look forward to The Hundred showcasing world-class cricket this summer."
Opener Warner, 34, was signed for £100,000 and all-rounder Stoinis, 31, for £80,000.
The first match of the new 100-ball competition - a women's fixture between Oval Invincibles and Manchester Originals - will be live on BBC TV on Wednesday, 21 July.
Both the men's and women's finals take place at Lord's on Saturday, 21 August.
- It's a mum-eat-mum world: Motherland returns for a third season of playdate politics and PTA terror
- You're Dead to Me: Was Lord Byron the most scandalous celebrity of the 19th century?