The visitors had to play the final few minutes of the crunch game with 10 men, with City going close to winning the game but for Gabriel Jesus' goal being ruled out for offside.
And Lampard was critical of Belgium international Fellaini.
SKY SPORTS
Frank Lampard says Marouane Fellaini must apologise to his Man United team-mates
He needs to apologise to his team-mates in the dressing room
Frank Lampard on Marouane Fellaini
"You can talk about Aguero, Aguero got in his face," he said on Sky Sports.
"There is some criticism there.
"(But) The forward motion, it's a headbutt.
SKY SPORTS
Frank Lampard was critical of Marouane Fellaini after his red card against Man City
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"He needs to go and speak to his team-mates who played for 80 minutes.
"He left them for 10 minutes, running around trying to defend with 10 men.
"He needs to apologise to his team-mates in the dressing room."