The Newcastle United midfielder has been a revelation since arriving at St James' Park from Olympique Lyonnais in January for €42.1 million.
Guimaraes has made 14 appearances across competitions this season, scoring three goals and providing two assists.
He has earned eight international caps for Brazil, scoring one goal, and many had expected him to be a starter at the FIFA World Cup.
However, Selecao boss Tite has opted to start Guimaraes on the bench, with West Ham United's Lucas Paqueta chosen to partner Manchester United's Casemiro in midfield.
It is a strong lineup for the nation, which many believe are the favorites to win the tournament in Qatar.
Alisson Becker starts in goal, with Danilo, Marquinhos, Thiago Silva, and Alex Sandro in defense.
As mentioned, Casemiro and Paqueta are in midfield and sit behind a scintillating attack.
The in-form Neymar, who has bagged 15 goals and 12 assists in 20 appearances for Paris Saint-Germain, is given a free-roaming role.
He also captains the side and is behind an attack consisting of Raphinha, Richarlison, and Vinicius Junior.
All eyes will be on how Tite's midfield performs, with many believing Guimaraes deserved to start.
Here are some reactions from fans on Twitter to the Newcastle midfielder's omission:
Brazilian legend and FIFA World Cup-winning captain Cafu predicts Selecao to win the tournament
Cafu, who captained the South Americans to the 2002 FIFA World Cup, has given his prediction for this year's campaign.
The AC Milan icon believes that Tite's men will triumph in Qatar due to their squad being the strongest since 2002.
He said (via the Daily Mail):
‘I think Brazil will win this year. This is the strongest group of players since 2002 and the team don’t rely too much on Neymar, like in the past. Brazil are strong in all areas: defence, midfield and attack."
It has been 20 years since Selecao last won the FIFA World Cup, and Cafu insists it is time for that to come to an end this time around:
"Twenty years without winning a World Cup or even without a final appearance is too much for Brazil. I believe this will end in Qatar."
The legendary right-back did touch on other potential favorites, such as Argentina and reigning champions France.
However, he feels that his nation are ahead of every other team:
"Brazil are ahead of every other team. But I think Argentina are very strong as well. They are playing well and Lionel Messi is a genius. France have the same team that won four years ago. These are the three favourites."