The club issued a statement that the decision to part ways was a "mutual" one. The Spanish coach was absent during Mumbai's 1-1 draw against Delhi Dynamos in New Delhi on November 6.
"The club has decided to part ways with assistant coach Oscar Bruzon with immediate effect. There have been differences in our football philosophy and both sides feel it's best to part ways amicably," Mumbai City FC CEO Indranil Das Blah said in the statement.
This was the second instance of a coach making an exit from an ISL side. Peter Taylor was sacked as head coach of Kerala Blasters on October 28 after a string of losses for the Kochi-based ISL team.
On his part Bruzon said he was proud of having been part of Mumbai City FC.
"Honour means respecting my club, its players, the owners and the fans. I am proud of what I have done for the club in the little time I've spent here and I know that the club feels the same way. I would like to conclude by saying that it's been an absolute honor and matter of pride being part of the Mumbai City FC family," he said.