Lens have completed a deal for Crvena Zvezda defender Milan Bisevac.
The 23-year-old will not arrive until January because of issues he has in Serbia.
Lens' financial director Francis Collado explained: "If we didn't sign him now we would never have been able to sign him in December.
"We have to prepare for the future. We are not sure he could play with us in August. If not he would join us during the winter transfer window."
Meanwhile, Crvena have announced the capture of international midfielder Aleksander Trisovic.
The 22-year-old has arrived from Ukrainian outfit Kryvbas Kryvyi Rih.
"We are delighted to have brought negotiations with Kryvbas to a successful conclusion and have Trisovic here. He is a player of extraordinary talent," president Dragan Stojkovic told Crvena's website.