Tottenham Hotspur had to come from a goal down to seal qualification for the Round of 16 as top of Group D.
Pierre-Emile Hojberg’s 95th-minute winner secured all three points for Spurs, but the injury to Son in the first-half marred what was otherwise a perfect evening.
After the South Korean’s head collision with Chancel Mbemba, he failed the concussion test and had to be substituted.
The 30-year-old winger could now miss Spurs’ crunch encounter with Liverpool on Sunday because of Premier League regulations for concussion-related injuries.
The Premier League and FA guidelines stipulates that a player who suffers a concussion must stay away from football activities for at least six days. This means Son would not be able to train until Monday.
“In the second half we had a good game and Clement scored an important goal in France in front of the French people and Pierre-Emile Hojbjerg is so important to confirm that top of the group,” captain Hugo Lloris reflected.
“It was a tough night, a great battle and even more psychological battle because we could feel in the first half a team was playing without the fear to lose, it was Marseille, and in the second half we had a team that was fearing to lose and it was us.
“Also I believe that when we had to face difficulties, we showed great personality and it’s a great result. Without our coach it was even more difficult for him in the stand and it’s a great winning team – that’s the most important thing.”