The Manchester City winger has spent the last year and a half on loan at Parkhead. He helped Brendan Rodgers’ side win the treble last season when he was a key member of the squad which was unbeaten in domestic competition.
Rodgers had hoped to sign the player and a fee of between £4 and £5 million was mooted.
However, City will have the final say on Roberts’ next move and may feel he would benefit from playing in the French league next season.
Nice finished third in Ligue 1 and, like Celtic, will play in Champions League qualifiers.
Roberts, 20, turned down the chance to play for England at the Under-20 World Cup so he could play for Celtic in the Scottish Cup final against Aberdeen.