The only viable answer from the more popular countries would Bjorn Borg and Sweden, and, obviously, Federer and Switzerland.
To those who say Nadal and Spain, they have no idea what football is in Spain.
Fed devotee (aka Rafa basher), you are yet again showing a lack of knowledge about Rafa.
Spanish sports newspapers' staffs surely know what is what in Spain. Rafa was
voted/named the greatest Spanish sportsman of all time by daily sports newspaper Marca (at the end of 2013) and of the last half-century by daily sports newspaper AS (at the end of 2017). The AS named him the greatest athlete of the last half-century because the newspaper celebrated its 50th anniversary.
Euroweekly, 04 January
2014: ¤¤
Rafael Nadal - Spain’s greatest sportsman of all-time.
RAFAEL NADAL was voted the greatest Spanish sports person of all-time. The winner of 13 Grand Slam titles and the current number one in the ATP world rankings, he received the award at the Gala for the 75th anniversary of the Spanish sports paper Diario Marca.
Chosen by readers of the aforementioned newspaper, Rafa finished a clear first, ahead of five-time Tour de France winner, Miguel Indurain with Pau Gasol, without doubt, the greatest Spanish basketball player of all time, third.
This is some achievement for Rafa, considering how many other famous Spaniards have graced the sporting world over the last 60 years, men like fellow tennis Open champions Manuel Orantes and Manuel Santana, top golfers Severiano (Seve) Ballasteros, Miguel Ángel Jiménez, Sergio Garcia and José Maria Olazábal, Formula 1 stars Fernando Alonso and Pedro de la Rosa, rally driver Carlos Sainz, former captain of the Spanish women’s national team Amaya Valdemoro, road cyclist Alberto Contador, Spain’s national football team coach, Vicente del Bosque, Real Madrid players Iker Casillas, Ricardo Zamora, Antoni Ramallets, Francisco Gento, Alfredo Di Stefano (a naturalised Spaniard), Sergio Ramos, Fernando Hierro and Raul Gonzales, the Barcelona midfield trio of Xabi Alonso, Xavi and Andreas Iniesta, plus Fernando Torres, David Silva, Telmo Zarra and Emilio Butragueño. ¤¤
https://www.euroweeklynews.com/sports/117987-rafael-nadal-spain-s-greatest-sportsman-of-all-time