Saints were claimed to be on the verge of deals for a few players this week, to add to their squad following the arrival of Mislav Orsic this month.
Southampton are having a tough time of it currently as they are bottom of the Premier League and will be looking towards the transfer window to lead to improvement in their form.
Doku, 20, has been with Rennes since the summer of 2020 but it has not been plain sailing for him in his time with the French club.
The Belgian winger has suffered from injuries this season and started just one match in the league, failing to score or assist.
Now Southampton have tested the water and asked Rennes about the winger, according to French outlet Foot Mercato.
Martin Terrier has suffered an ACL and he is not expected to return until next season, which is expected to lead the French club to relying on Doku more.
Thus they are not desperate to sell Doku and it remains to be seen if, after the enquiry, Southampton persist and pursue the winger.
