Leinster captain Isa Nacewa and fellow New Zealander Jamison Gibson-Park have been denied entry to South Africa because of visa problems.
It is understood they did not have the visa New Zealanders require to enter the country when they flew in to play two Pro14 games in South Africa.
They will return to Dublin "at the earliest opportunity" and Nick McCarthy is flying out as a replacement.
Leinster are to play the Southern Kings and the Cheetahs in the Pro14.
The Irish province face the Southern Kings at the Nelson Mandela Bay Stadium in Port Elizabeth on Saturday followed by the Cheetahs at Free State Stadium in Bloemfontein on Friday, 22 September.
Nacewa and Gibson-Park were refused entry on their arrival by customs at Tambo International Airport in Johannesburg.
South African law changed at the beginning of the year to require citizens from New Zealand to have a visa, where previously none had been needed.
Fiji international Nacewa is a versatile back while Gibson-Park and McCarthy are both scrum-halves.