Adolfo Daniel Vallejo (born 28 April 2004) is a Paraguayan professional tennis player. He has a career-high ATP singles ranking of No. 99 achieved on 16 March 2026 and a doubles ranking of No. 435 reached on 21 April 2025. He is currently the No. 1 singles player from Paraguay.
He reached an ITF junior combined ranking of world No. 1 on 15 August 2022.
Vallejo represents Paraguay at the Davis Cup, where he has a winâÂÂloss record of 5âÂÂ3.
Vallejo had remarkable results on the ITF junior circuit, maintaining a 107âÂÂ38 singles win-loss record. In 2021, he won the prestigious Orange Bowl in Plantation, United States, defeating American Bruno Kuzuhara in the final. He was the first Paraguayan player to win that event and only the second to reach the final after VÃÂctor Pecci.
In January 2022, he was a runner-up in the boys' doubles category at the 2022 Australian Open, with American Alex Michelsen. The pair lost to second seeds Bruno Kuzuhara and Coleman Wong in the final.
In July 2023, Vallejo reached his first final on the Challenger Tour in Santa Fe, Argentina, losing to Mariano Navone in the final. The following month, he won his first Challenger doubles title in Lima, Peru, partnering with Gonzalo Bueno, defeating Jorge Panta and Ignacio Buse in the final.
In March 2024, Vallejo won his first Challenger title in São Léopoldo, Brazil, defeating Enzo Couacaud in the final. He became the youngest Paraguayan to win an ATP Challenger title and the fourth Paraguayan champion in ATP Challenger Tour history and first since Ramon Delgado in 2009. As a result, he reached the top 300 on 6 May 2024.
In March 2025 ranked at a career-high of No. 187, achieved on 17 March 2025, Vallejo reached the semifinals at the home Challenger in Asunción, Paraguay but lost to eventual champion Emilio Nava. Following winning the 2025 Guayaquil Challenger, Vallejo reached the top 150 in the singles rankings at world No. 143 on 24 November 2025.