The 20-year-old has spent his entire career with Santos, but he is now keen seek pastures new and challenge himself in Europe following the club's relegation from the Brazilian top flight.
Last month, Leonardo's agent Rafaela Pimenta stated that "the time has come" for her client to move to Europe in the January transfer window amid interest from a number of clubs, including some from the Premier League.
Arsenal allegedly submitted an offer of €20m (£17.2m) plus bonuses for Leonardo towards the end of last year, while Newcastle United are understood to have held talks with Santos to discuss the striker's availability.
Man United and Brentford have also been credited with an interest along with Serie A pair Roma and Lazio, but all of these clubs appear to have lost out in the race for the youngster's signature.
According to journalist Fabrizio Romano, Portuguese giants Benfica have reached an agreement with Santos to sign Leonardo for an initial €18m (£15.5m) plus bonuses.
Leonardo is said to have "already accepted" the move to Benfica and the striker is due to fly to Lisbon within the next 24 hours to complete his medical and sign the necessary paperwork.
Since making his professional debut for Santos in 2020, Leonardo has established himself as one of the brightest prospects to emerge from South America.
The striker has scored a total of 54 goals in 168 appearances for Santos across all competitions, including 21 strikes in 49 games during the 2023 campaign.
At Benfica, the Brazil Under-23 international is set to provide competition in attack for compatriot Arthur Cabral, a summer signing from Fiorentina, as well as Petar Musa and Casper Tengstedt.
Although Man United look set to miss out on signing Leonardo, Erik ten Hag's side are understood to have a number of other strikers on their radar, including RB Leipzig's Timo Werner, Bayern Munich's Eric-Maxim Choupo Moting and Stuttgart's Serhou Guirassy.
Arsenal, meanwhile, have been tipped to splash he cash on a high-profile centre-forward, with Napoli's Victor Osimhen, Inter Milan's Lautaro Martinez and Bayer Leverkusen's Victor Boniface all said to have been identified as possible alternatives to top target Ivan Toney of Brentford.