The Portugal international was strongly linked with a move away from Lille over the summer, but the transfer window closed with the midfielder still at Stade Pierre-Mauroy.
The 24-year-old has struggled with a knee injury this season, making just two appearances, but he did feature in his side's last game against Marseille before the international break.
Liverpool are still believed to be interested in Sanches, and Letang has confirmed that the Portuguese is still available for transfer in 2022.
"I have already spoken about it," Letang told BFM Lille. "I have already discussed with him, if an offer from a big club arrives, Renato will be able to leave. We will see what will happen.
"But for now, he is with us and he is happy to be. We saw that he had been able to show an interesting level of performance during his return from injury at the end of the season, but also at the Euros with Portugal."
Sanches's current deal with Lille is due to expire in the summer of 2023. body check tags ::