Leinster's preparations for their Guinness Pro 14 game with Southern Kings have been thrown into disarray.
Isa Nacewa and Jamison Gibson-Park were denied entry to South Africa after touching down.
The Leinster pair are New Zealand passport holders, and the club did not apply for a visa in time.
Nick McCarthy has flown out as cover for the games with Southern Kings and Cheetahs.
The province blamed an "administrative oversight."
Guy Easterby, Head of Rugby Operations, Leinster Rugby who is in South Africa with the squad said:
"As of 16 January 2017 a visa is required for New Zealand nationals entering South Africa.
"Unfortunately this visa was not applied for by Leinster Rugby on behalf of Jamison Gibson-Park and Isa Nacewa in advance of the squad leaving Dublin Airport on Tuesday afternoon. 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.
"Nick McCarthy will arrive in later today and for the moment no other player will be called up to the squad.
"The squad is looking forward to the considerable challenge that awaits them against the Southern Kings.”