However, work permit issues - a consequence of having never played top-flight football and being without a senior Brazil cap at the time - led to his short-term return to former club Vasco da Gama.
That came with the understanding that he would link up with Chelsea in time for pre-season, and Santos featured for 195 minutes for Mauricio Pochettino's side during the pre-season tour of the USA.
Rather than remain at Stamford Bridge, Santos was loaned out to Nottingham Forest, but he has made just one start in the EFL Cup and one brief substitute outing in the Premier League, and as expected, Chelsea are not happy.
With a break clause included in their deal with Forest, Chelsea will likely recall the 19-year-old, but their options for alternative destinations in January will be limited.
Chelsea have filled their seven foreign loan spots and only academy players are exempt when facilitating temporary moves abroad, like in the case of Charlie Webster who is at Heerenveen.
All in all, it leaves Chelsea with only English clubs to choose from when it comes to finding a suitable home for Santos for the second half of the season. Here, Sports Mole identifies five potential destinations.
On the back of being out of favour at Forest, it is debatable whether it is plausible for Santos to move to a club of Newcastle's standing, yet it is something that may suit all parties.
Newcastle require a short-term alternative for Sandro Tonali. The likes of Ruben Neves and Kalvin Phillips have been linked, but that will come with a cost at a time when the Magpies must continue to meet FFP criteria. They may also need to strengthen in more than one area.
This transfer may only really work if Newcastle are able to secure European football for after Christmas with Santos facing an uphill task to become a regular starter in what would be a short period under Eddie Howe.
Nevertheless, the two clubs have already conducted good business with Lewis Hall and are familiar with how the other operates. The main downside, however, is that it would fill Newcastle's second domestic loan slot, something that they may prefer to use on a Premier League-proven player.
Allowing Santos to move down the King's Road to Fulham may also make sense, particularly if the Cottagers find themselves in a position where they could sell Joao Palhinha.
That situation with Bayern Munich remains up in the air and if Marco Silva requires a replacement for the Portugal international, he may prefer someone with similar physical characteristics rather than the more diminutive Santos.
Comparisons can be made with the Forest move, yet Santos may be more suited to Silva's philosophy over Cooper's. Fulham also have two domestic loan slots available for January.
There are other options in the Premier League, but it is questionable whether any team competing in a relegation battle will feel comfortable throwing a 19-year-old Brazilian into their engine room with 97 minutes of English football under his belt.
That means that Championship clubs come into the equation for a player who only played 424 minutes of top-flight football in Brazil. Furthermore, Chelsea had no issues allowing Cesare Casadei to move to Leicester City, rather than taking on a spell in Serie A.
Leicester, as well as Leeds United, are probably out of the question, but Southampton may come into the equation if Chelsea deem Russell Martin's style of play to be ideal for Santos.
Martin is not short of options in the centre of the pitch, yet there are players who may attract offers from elsewhere in January, freeing up space for Santos to gain regular football in a promotion battle, just like Casadei.
The same applies to Sunderland who have already done business with Chelsea regarding a loan deal for Mason Burstow.
There is an argument that Tony Mowbray is operating with a young squad as it is. The majority of his current crop are below 24 years of age and they may prefer experience over another prospect on their books.
On the flip side, acquiring the services of someone like Santos would allow for more rotation in a side that has been relatively settled, with Mowbray having seven players who have started at least 15 of their 16 league matches so far this season.
Granted, this is something of a left-field choice, but the appointment of Joe Edwards as head coach will change perceptions of Millwall.
The former interim England Under-20s manager has already earned a 4-0 victory away at Sheffield Wednesday in his first match and will have his eyes on several young talent ahead of January.
Edwards's previous association with Chelsea can also not be understated. The 37-year-old never got to work with Santos during his time at Stamford Bridge, but there will an element of trust between him and Chelsea's recruitment team.
Although it may be more plausible that some of the Chelsea academy players that Edwards is more familiar with may make the switch to The Den, Santos will enter the conversation if a new home needs to be found.