The ex-Brazil international believes his fellow countryman has been brought to the French capital as part of Carlo Ancelotti's long-term vision for the club
The Sao Paulo winger will move to the French capital in January 2013 for a reported club record fee of £35 million (€45m), and Rai has responded to claims that the 20-year-old should have signed for a more established European club.
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"They are investing a lot, but the signing of Lucas is no longer one in a series," he explained to Globo Esporte.
"They try to play on the counterattack and it fits Lucas as he has blazing speed with the ball and was bought for that purpose.
"I think he will come and play, but on the other hand cannot just be accommodated because there are many good players in the squad."
Rai also revealed that his close friend Leonardo, who is now Les Parisiens director of football, was instrumental in persuading his compatriot to join the club.