Inter maintained their unbeaten start to Group F but were booed off after being held to a goalless home draw by St Etienne on Thursday evening.
The out-of-sorts Italian giants could not find the breakthrough in an evenly-fought encounter at the San Siro and dropped their first points in the Europa League group stages.
Walter Mazzarri's side remain at the top of their group with seven points, four more than St Etienne after three games played.
However, the Nerazzurri left the pitch with boos from a large section of the crowd ringing in their ears after failing to win for a third straight game in all competitions.
Inter, who have not conceded a goal in the group stages, went into the contest unbeaten in eight European home games prior to the encounter in Milan.
They had the better of the early exchanges and could have taken the lead in the 17th minute when former St Etienne player Fredy Guarin drilled in a 30-yard effort, but Stephane Ruffier was equal to the task.
Inter wasted a good chance to go in front a minute later when Mauro Icardi, having been set up by Mateo Kovacic inside the box, fired well wide.
St Etienne almost made the hosts pay for that wasted opportunity midway through the first half when Kevin Theophile-Catherine's close-range header from Franck Tabanou's dangerous cross almost crept inside the post.
The visitors gained in confidence and before half-time Inter goalkeeper Juan Pablo Carrizo was called upon to keep out Tabanou's well-struck shot from outside the area.
The home side were back on the attack in the second half, though, and went close to breaking the deadlock after the hour mark when Zdravko Kuzmanovic forced Ruffier into a full-length dive to keep out his left-footed shot as it arrowed towards the far post.
Inter survived another scare in the 70th minute when Romain Hamouma found space in the box and struck a shot that was saved by Carrizo.
The home side resumed their bid for the opening goal and, with eight minutes remaining, Nemanja Vidic's header from Hernanes' cross went wide, much to the disappointment of the increasingly frustrated home fans.
Hernanes had the last chance of the game when he drilled in a powerful effort from outside the area, but that was saved by Ruffier as Inter were forced to settle for a point.