Bassong is set to leave Metz after they were relegated from France's top flight last season. The Lorraine club finished bottom of Ligue 1 with a total of 24 points from 38 games.
The 22-year-old has previously been linked with Premier League rivals Everton.
The Paris-born player has made 79 appearances for Metz over the last three seasons and scored one goal after graduating from the club's B team. He played 19 times for the club during the last campaign.