Pellegrini dropped Hart for Saturday's Premier League defeat of Norwich and his replacement Costel Pantilimon will continue against CSKA Moscow in the Champions League this week.
The England goalkeeper has paid the price for a number of high-profile errors over the past year for both club and country.
This season alone he has made costly mistakes against Scotland, Aston Villa, Bayern Munich and - most recently - Chelsea.
With pressure growing, Pellegrini felt the time had come to make a change but he been impressed by the player's reaction.
Pellegrini said: "I think Joe has reacted very well. He is a professional player.
"For him it is also a good thing to have a rest after playing so many matches.
"He is working without any problem, supporting Costel Pantilimon.
"Nobody wants to be out but he thinks it will be useful for him."
Hart has been City's number one since being unexpectedly promoted ahead of Shay Given in 2010.
For most of that time he has been outstanding and it is only in the past 12 months that regular errors have crept into his game.
Pantilimon has had to wait patiently for an opportunity since being brought in as Hart's deputy in the summer of 2011, featuring only in domestic cup ties until Saturday.
The Romanian's belated Premier League debut proved rather uneventful from his point of view as City romped to a 7-0 win and were hardly tested defensively.
On that basis, Pellegrini will not be reversing his decision as City bid to claim a place in the Champions League last 16 at the expense of the Russians.
The Chilean said: "I don't know when Joe will come back to the team. It is very important for him to have a rest.
"He has played all the matches for two-and-a-half years.
"We will see in the future what we must do. For today, Pantilimon is playing."