Juventus midfielder Vidal underwent meniscus surgery in May and is a major fitness doubt for Jorge Sampaoli's side, who begin their FIFA World Cup campaign on Friday.
However, while Diaz is a huge admirer of Vidal, the former has stressed that no one player is more important than the whole team.
"Vidal is one of the best players in the world and we all know the strength he brings to the team," said Diaz at a press conference.
"But we are a team and we all play with the same hopes and dreams. The team is stronger than any player."
Should Vidal not make it, then Felipe Gutierrez is thought to be in line to join Diaz in Chile's midfield.
And Diaz feels that the FC Twente man would be a more than competent replacement.
"He (Gutierrez) is a player of great condition and is very experienced," Diaz added. "He's playing in Europe and earned a place (in the squad)."
