The 19-year-old attacker looked likely to move to Old Trafford until the French side's big-money move was confirmed on Wednesday, much to the amazement of United boss Sir Alex Ferguson.
And Lucas' representative Wagner Ribeiro has admitted that negotiations with the Premier League side had reached an advanced stage.
"Everything was agreed between Sao Paulo and Manchester United," Ribeiro told UOL.
"The contract had been written and just needed to be signed. But then Leonardo called me and asked to talk to Lucas.
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"They talked. Leonardo was helped by the fact he is Brazilian. He was very gentle with Lucas.
"The possibility of living in Paris - a much more pleasant city than Manchester - also influenced his decision. But it was PSG's project that impressed Lucas."
Ribeiro also explained the lengths he had gone to in order to seal his client's move to the Parc des Princes club.
"I'm just a worker," he added. "I've not been able to sleep for five days here in Europe. I can't rest and I miss my son.
"I boarded a plane at 5am in Manchester and arrived in Paris this morning to finalise everything with Leonardo.
"But what gives me the taste of victory is that I know Lucas is happy."