After a productive pre-season with the Blues in the United States where he accumulated 196 minutes across four matches, Santos had hoped to remain as part of Mauricio Pochettino's squad at Stamford Bridge.
However, the arrival of Lesley Ugochukwu threw a spanner in the works, Pochettino choosing to retain the young Frenchman over Santos.
The collective decision was made for the then-19-year-old to spend the campaign at Forest, the hope and expectation being that he would become a mainstay in the engine room.
Instead, the former Vasco Da Gama starlet endured a discouraging stint in the East Midlands, his only start coming in an EFL Cup defeat to Burnley and solitary Premier League appearance being a seven-minute outing at Liverpool when Forest were already 3-0 down.
To add to his frustration, Santos did not feature in any squad between November 12 and December 30, making it inevitable that Chelsea would activate their break clause at the turn of the year.
"He was praising me a lot"
In an exclusive interview with Premier League Brasil where he gave his view on a range of moments in his young career, Santos hinted that he was left perplexed over failing to earn a chance under Cooper - and later Nuno Espirito Santo - when he had been receiving positive feedback over his efforts in training.
The Brazil international said: "There's no way we can predict what's going to happen. But I was always well, willing to help and making a difference in training, so much so that the coach at the time, Steve Cooper, was praising me a lot in training,
"Unfortunately he didn't give me any opportunities. I was at my peak both physically and technically."
Upon returning from international duty with Brazil Under-23s, Santos went back out on loan to Strasbourg, which proved to be far more beneficial than his period with Forest.
In his first two starts in Ligue 1, Santos helped Strasbourg to wins over Nantes and Rennes, and it led to him being named as the division's young player of the month for March.
Commenting on his time in France, he added: "It was the right choice. I was able to show my football to Europe. It was a very good sequence to show my potential."
What next for Santos?
New Chelsea head coach Enzo Maresca has seemingly taken the approach that he will hand all of Chelsea's heavily-populated squad a chance to showcase their qualities during the early weeks of pre-season.
However, the addition of Kiernan Dewsbury-Hall and likely integration of Romeo Lavia will not help Santos's chances of earning regular game time at Stamford Bridge.
With Santos holding a contract until 2030, Chelsea's hierarchy can afford to be patient over his development, and a season-long loan at a Premier League team or club in a high-profile European league looks the most likely outcome.