Chelsea signed the 19-year-old midfielder from Brazilian outfit Vasco da Gama in January this year, with Santos a highly rated talent.
He returned to Vasco da Gama in March on a short-term loan deal, before then being loaned to Nottingham Forest for the season in August.
Chelsea are looking for Santos to play as much as possible at the City Ground under Steve Cooper.
However, Cooper has given Santos only seven minutes of Premier League football so far and Chelsea have a clause they can trigger.
Even though Santos played the full 90 minutes against Burnley in the EFL Cup, Chelsea want him to play more.
And they also have the option to end his loan early with the Tricky Trees if they do not play him a certain number of matches.
Given Santos’ situation, Nottingham Forest are currently running the real risk that the 19-year-old will be taken back to Stamford Bridge in January.