The French-born Senegalese international spent the second half of last season on loan at Al-Ahli in Saudi Arabia after falling out of contention with his Ligue 1 club.
Niang joined Rennes from Torino in 2019 after previously spending six years on the books of Italian giants Milan.
Venezia are said to be the favourites for his signature this summer, though Celtic Fenerbahce and Shanghai Shenhua are all pursing the player, reports Foot Mercato.
Meanwhile, Celtic target Ko Itakura has stated it's his desire to play for “a world famous club” as the Japanese international looks set to leave on loan again this summer.
The Manchester City defender spent the last two seasons on loan at Groningen and Celtic are trying to convince the EPL champions his next stop should be in Glasgow. According to the Daily Record, however, City have set a hefty asking price for a season-long loan.