Right-back - Gonzalo Montiel (River Plate)
Argentina's Gonzalo Montiel has spent his entire career with River Plate and is now slowly establishing himself as a regular in the La Albiceleste setup.
Montiel will be competing with Udinese's Nahuel Molina for the right-back spot in the semi-final of Copa America 2021. The RIver Plate right-back is a highly-rated player who has won nine caps for his national side, but both Molina and Montiel are not much experienced.
The 24-year-old Montiel has been linked with moves to Lyon and West Ham United in recent weeks. So a strong showing in the remainder of Copa America 2021 could increase interest in him.
Centre-back - Cristian Romero (Atalanta)
Cristian Romero's fitness remains a big question after the centre-back missed Argentina's Copa America 2021 quarter-final against Ecuador.
Fiorentina's German Pezzella took his place, but Argentina would benefit with the return of Romero. The 23-year-old is regarded as one of the best young centre-backs in Serie A. His performances have piqued the interest of clubs like Manchester United.
Romero is good on the ball and strong defensively and will likely start if he is fully fit. Colombia's attack could cause fewer problems with Romero in Argentina's defence.
Centre-back - Nicolas Otamendi (Benfica)
Nicolas Otamendi has been the first-choice centre-back for Argentina for some time now. He will likely start the Copa America 2021 semi-final, barring any unfortunate injury.
Otamendi's style of defending has often raised question marks, but it is difficult to deny the centre-back's quality. Otamendi was a crucial cog in Pep Guardiola's Manchester City, making 210 appearances in all competitions before joining Benfica last summer.
The 33-year-old has won 78 caps for Argentina and is one of their more experienced players in their Copa America 2021 squad.
Left-back - Marcos Acuna (Sevilla)
Argentina manager Lionel Scaloni will have to choose between Ajax's Nicolas Tagliafico and Sevilla's Marcos Acuna for the Copa America 2021 semi-final; Acuna is likely to get the nod.
Tagliafico did not enjoy the best of seasons with Ajax and has struggled in Copa America 2021 as well. Acuna, meanwhile, enjoyed a decent debut season with Sevilla, making 26 league starts as a left-back.
The 29-year-old, who joined Sevilla from Sporting CP last summer, is a good crosser and a consistent performer. Acuna started in the quarter-final and should be in Argentina's first XI for the semi-final.
Other options: Nahuel Molina (Udinese), German Pezzella (Fiorentina), Lucas Martinez Quarta (Fiorentina), Lisandro Martinez (Ajax), Nicolas Tagliafico (Ajax).