The 20-year-old is widely regarded as one of the brightest prospects in Brazil and has developed into a star player for Santos since making his professional debut in 2020.
Leonardo has recorded 54 goals and 11 assists in 164 appearances for the Brasileiro giants across all competitions, netting 21 times in 45 games in 2023.
The Brazil Under-23 international was strongly linked with an exit from Santos last summer, with Serie A pair Roma and Lazio understood to have held advanced talks with the striker.
A switch to Italy ultimately failed to materialise for Leonardo and he has since been tipped to make a move to the Premier League, as a number of English clubs are believed to be keen to win the race for his signature.
Last month, Newcastle allegedly held talks with Santos to discuss the availability of Leonardo, while Man United are understood to have identified the Brazilian as a possible alternative to Ivan Toney.
Arsenal and Brentford have also been credited with an interest in Leonardo and each of the potential suitors have seemingly received a boost in their pursuit of the youngster heading into the New Year.
Speaking to the Italian media, as quoted by the Evening Standard, Leonardo's agent Rafaela Pimenta said: "Already in the previous transfer market he had the possibility of being sold, but Santos' sporting situation was very particular.
"He agreed to stay because he wanted to help out until the end of the championship. He didn't want to leave because it wasn't the right thing to do.
"But the time has come to move. He wants to have a European experience and his time will come this winter."
Although Man United are believed to be prioritising the signing of a new centre-back, the Red Devils have also been tipped to bolster their options in attack to ease the pressure on summer addition Rasmus Hojlund, who is yet to score in the Premier League this season.
Arsenal boss Mikel Arteta could also look to delve into the winter-window market for a new forward amid Gabriel Jesus's recent injury concerns, although the addition of a new midfielder is said to be high on the club's radar according to former Gunner Gilberto Silva.
As for Newcastle, Eddie Howe is expected to be active in the New Year having been forced to work with a depleted squad in recent weeks due to several injuries, and the potential addition of Leonardo could provide competition in attack for both Alexander Isak and Callum Wilson.
It is thought that Santos would demand a figure between €20m (£17.5m) and €25m (£21.9m) to part ways with Leonardo in January.