Tevez could return to first team action against Chelsea at Eastlands on Wednesday, where a victory for longtime Premier League leaders City will see them move to within a point of reigning champions and current table-toppers Manchester United.
The Argentina striker has not played senior football for City since Mancini accused him of refusing to warm-up during a Champions League loss away to Bayern Munich in September.
The 28-year-old then spent more than three months in Argentina without City's permission before returning to northwest England after failing to secure a move during the January transfer window.
Tevez though has since apologised to Mancini and has recently played two matches for the reserves.
But former City player Marsh told BBC radio on Wednesday: "Mancini will be sacked if Tevez plays and City don't win the title.
"I believe strongly that, if Chelsea win tonight, City won't win the title."
On Tuesday, Mancini said it was "possible" the 28-year-old Tevez would be on the bench for the Chelsea game.
But Marsh, who was a then record ?200,000 signing for City in 1972, said Tevez's return could disrupt the team's harmony at a crucial stage of the season.
"At this moment in time they have got a fantastic squad of players -- (Sergio) Aguero, (Mario) Balotelli and (Edin) Dzeko up front, (David) Silva and (Samir) Nasri.
"If he should change it and bring in Tevez and they lose it I think it will be that important.
"Since Tevez allegedly refused to come on in that game in Germany, Manchester City have been knocked out of every competition.
"If they should also lose the Premier League based on the fact he is coming back I think that is a bridge too far."
Tevez's situation has been compared to that of Marsh, now 67, when he joined City from Queens Park Rangers.
Back then City were four points clear at the top of the old First Division but went onto finish fourth.
"The comparison is different," Marsh said. "Carlos Tevez has played for City before. I came in from the cold.
"I was kind of a jinx all those years. My debut was 40 years ago this Sunday. The game was against Chelsea and we won 1-0.
"If he (Tevez) plays tonight and City win 1-0, I will start believing I am a jinx," said Marsh, who scored 36 goals in 118 appearances for City.
Source: AFP
Source: AFP