Warnock has revealed that Payero, 22, has passed his medical and will join Boro from Argentine club Banfield following his participation with Argentina at the Tokyo Olympics.
Boro have been in discussions with other clubs from South America about potential signings, with chief executive Neil Bausor leading the conversations.
When asked if the Teessiders’ could sign other players from the continent, Warnock replied: “I don’t want more than two.
“We are looking at another couple of Brazilians and Argentinians, but whether we get them or not.
“They are difficult to get over the line but Neil is dealing with all that.
“It’s only the financial details which are a minefield abroad.”
Boro coach Leo Percovich also has contacts in South America, which have proved helpful when looking at players from the continent.
Warnock also says Boro chairman Steve Gibson is keen to sign players from overseas if a deal can be agreed.
When discussing how the Payero deal came about, Warnock added: “The recruitment guys gave it to us and then Leo looked into it.
“Steve, for all we haven’t got a lot of money, he always wants to gamble with the Argentinians and the Brazilians.
“He (Payero) is young, a good age, going to the Olympics so it may not be a bad gamble.”
“The lad is happy and the medical is passed. In the Olympics squad it says Middlesbrough which is a good sign.”