Arsenal held off competition from Wolverhampton Wanderers to sign Marquinhos during the summer transfer window, according to Italian journalist Fabrizio Romano.
The 19-year-old made the move to the Emirates Stadium from Sao Paulo in July, and he impressed on his debut for the Gunners against Zurich in the Europa League last week.
The attacker both scored and provided an assist in his side's 2-1 victory, and he will now be bidding to earn minutes in the Premier League.
Marquinhos was not involved in the squad in the early stages of the campaign but has recently been on the bench against Fulham, Aston Villa and Manchester United in England's top flight.
Romano has claimed that Wolves were also keen to sign the Brazilian over the summer, but the presence of the London club's technical director Edu put the Gunners at the head of the queue.
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The journalist also claimed that Arsenal are taking a keen interest in "the Brazilian market", with Edu boasting a number of strong relationships with senior figures in his home country.
"Marquinhos scored his first Arsenal goal this week in the Europa League following his €3.5m (£3m) move to the Emirates Stadium in the summer. In my view, this could end up being a smart piece of business and a real bargain," Romano wrote in his column for CaughtOffside.
"Wolves wanted Marquinhos too, but Arsenal have been faster thanks to Edu's relationship with Sao Paulo. Arsenal are convinced he's a top talent for present and future, and for sure the club will keep following the Brazilian market as Edu has great relationships there."
Marquinhos made 42 appearances for Sao Paulo during his time with the Brazilian outfit, contributing four goals and three assists in the process.
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Arsenal have not been in Premier League action since the 3-1 loss at Man United on September 4, with the latest set of league fixtures being postponed following the death of Queen Elizabeth II.
The Gunners are set to continue their Europa League campaign on Thursday evening at home to PSV Eindhoven before facing Brentford in the league next weekend.
However, the clash with the Bees is in doubt due to the Queen's state funeral, which could also see the next set of Premier League matches postponed until a later date.
As a result, Mikel Arteta's side might not be back in action in England's top flight until October 1, when they will welcome Tottenham Hotspur for a North London derby.