Mariano was sold by Real this summer and has kicked off his career in Ligue 1 in stunning form.
However, the striker admits he still harbours an ambition to return to Madrid.
He told Cadena Ser: "I try to do the best for OL and after that will be what God will want. Going back to a big club like Real Madrid would be a dream."
Mariano was rated highly by Real coach Zinedine Zidane, who was reluctant to lose him over the summer.