Leinster have accepted responsibility after captain Isa Nacewa and fellow New Zealander Jamison Gibson-Park were refused entry to South Africa.
The pair will miss the Irish province's upcoming PRO14 fixtures against the Southern Kings and Cheetahs having been turned away after arriving in Johannesburg without the necessary visas.
"Unfortunately this visa was not applied for by Leinster on behalf of Jamison Gibson-Park and Isa Nacewa in advance of the squad leaving Dublin Airport on Tuesday afternoon," head of operations Guy Easterby admitted.
"It was only brought to our attention upon landing into Johannesburg on Wednesday morning that this was now a requirement. This was clearly an administrative oversight on our part and a valuable lesson has been learned."
New Zealanders were previously exempt from having to obtain visas to enter South Africa but the policy was changed in January.
"Nick McCarthy has been called up to the touring squad," Leinster confirmed in an earlier statement.
The Southern Kings and Cheetahs are competing in the PRO14 for the first time this season and both sides have lost their opening two fixtures.