Asian Cup champions and 2022 World Cup hosts Qatar have one point from two games and are ahead of Argentina on goal difference in Group B, with third spot potentially enough to progress to the knockout phase.
The pressure is on Messi and Argentina to avoid a group-stage exit and Qatar head coach Sanchez insisted his side will not be overawed by the five-time Ballon d'Or winner.
"It's true we are not very well known in South America, but we have super-professional players and we've come to compete, not to take photos with Messi," Sanchez told reporters.
"They're the favourites and are obliged to win. We'll try to compete against a great team who have the best player in the world.
"We have a chance to qualify and that's what's exciting, not the fact we could knock out a monster like Argentina."
Qatar, meanwhile, overturned a two-goal deficit to draw 2-2 against Paraguay before suffering a late 1-0 loss to Colombia on matchday two.
Sanchez added: "Messi can be decisive in any game due to his quality, hundreds of coaches have spent ages trying to stop him but there's no magic formula, it all depends on Leo's feet.
"However much you focus on it it's very difficult to stop him, but we'll try to prevent him from getting involved in the play in the final third of the pitch."
Qatar are one of two teams from the Asian Football Confederation invited to compete in the Copa America this year, with Japan needing a result against Ecuador on Monday to be left with any chance of making the knock-out stages.