City face a testing eight days with this weekend's Premier League clash against Aston Villa followed by a crucial Champions League game at home to Villarreal and then the Manchester derby.
With several players only returning from international duty on Thursday, Mancini is concerned about fatigue and expects others to step forward.
Hargreaves, bidding to resurrect his career after three injury-ravaged years at Manchester United, is therefore in contention having worked further on his fitness since a goalscoring debut in last month's Carling Cup defeat of Birmingham.
Mancini said: "We don't have any players injured but we have four or five players very tired. For Aston Villa we will put off some players that are more tired, they will probably stay at home.
"It is important to have a team of players who are ready to fight in every moment."
He added: "Hargreaves is ready to play. Maybe not one (full) game but he is ready."
Hargreaves, 30, who was released by United last summer, played 57 minutes in what was his first competitive match for 10 months against Birmingham.
Striker Sergio Aguero will not be risked by Mancini despite making a good recovery from the groin injury suffered against Blackburn on his last outing.
Fellow forward Mario Balotelli has overcome a back problem and is set to play while controversial forward Carlos Tevez is highly unlikely to feature as disciplinary proceedings continue.
Mancini added: "It is important at the moment to have all the players because we play every three days for one month until the next international break.
"It is also very important to have all the players because I can change every game."
City are joint top of the table after a flying start to the season but Villa will travel to the Etihad Stadium with their own unbeaten record to protect.
Alex McLeish's side trail City by eight points but have proved difficult to beat and Mancini feels the players he selects will have to be on top form.
He said: "It will be very hard. They are good team, they have not lost any games.
"It is important we finish the game with a victory but it will be very hard and we need to play very well.
"I think Alex is a good manager. He knows the Barclays Premier League very well and he has more experience."
Mancini at least has no fears over the form of Spaniard David Villa, who continued his fine start to the campaign with two goals against Scotland in midweek.
He said: "I think he is one of the best players in the world - and for him it is difficult to play all the games.
"I think he has improved a lot in the last year."
Mancini is wary of the threat posed by a number of Villa players, not least former City duo Shay Given and Stephen Ireland.
Republic of Ireland goalkeeper Given joined Villa in the summer after losing his place to Joe Hart during a frustrating final season at City.
Ireland left on bad terms just over a year ago as part of the deal which took James Milner in the opposite direction.
When asked during his pre-match press conference whether the pair would have a point to make, Mancini said: "Sure, I think that.
"It is normal, they come to Manchester again and want to do a good job.
"I think Shay will want to have a good game, he is a good keeper.
"(Darren) Bent is a good player, (Gabriel) Agbonlahor is a good player, (Charles) N'Zogbia is a good player, Ireland is playing very well. (Stiliyan) Petrov.
"They are a good team. They have improved from last year.
"They have started the season very well and I think it will be a tough game."