At the turn of the year, the Premier League giants finalised the signing of the midfielder, who starred for Vasco da Gama in the Brazilian second tier in 2022.
Although winning the race for the 18-year-old was regarded as a coup, it came with its complications as there was no guarantee that the teenager could make an immediate start to life at Stamford Bridge.
Those concerns have been on the backburner while Santos represented his country at the Under-20 South American Championship, emerging as the star of the tournament.
Despite being a central midfielder, Santos finished the competition as joint-top goalscorer alongside teammate Vitor Roque, another prospect being linked with a switch to England.
Recent reports have indicated that Chelsea were confident that the player showcasing his ability in an international tournament would help their case when making a second application for a work permit.
However, according to Nizaar Kinsella of the Evening Standard, Chelsea have learned that Santos still does not fulfill the necessary criteria to play competitive matches for the West Londoners.
That development comes as a considerable blow to both player and club with Santos said to want to spend the upcoming months making the transition to life in England.
Instead, it appears that a loan switch back to his homeland is the most likely outcome, with Santos yet to play in the top flight in Brazil.
At a press conference on Friday, head coach Graham Potter admitted that Chelsea are currently assessing what the best short-term option is for Santos.
As per journalist Bruno Andrade, Palmeiras and Internacional are the leading contenders to sign the player, who is being tipped to eventually break into the senior Brazil squad.
Corinthians are also said to be outsiders for Santos, with all three clubs due to participate in the 2023 Copa Libertadores.
That is an important factor for Chelsea with playing in a continental competition earning more points towards successfully reaching the work permit threshold.