Pellegrini strongly criticised Swedish referee Jonas Eriksson and appeared to question his impartiality after a match which turned on the decision to award Barca a penalty and send off City defender Martin Demichelis in the 54th minute.
"UEFA has mandated a disciplinary inspector to commence an investigation concerning the press interviews given by the Manchester City FC head coach Manuel Luis Pellegrini to media after the above-mentioned match," a UEFA statement said.
"Based on the outcome of this investigation, a decision will be taken on whether disciplinary proceedings will be opened."
Speaking after Tuesday night's match, Pellegrini said: "From the beginning I felt the referee was not impartial to both teams.
"I think it was not a good idea to put a referee from Sweden in charge of such an important match, especially a referee who has made an important mistake against Barcelona in a previous match.
"[It's] more important football in Europe than Sweden. A big game with two important teams, that kind of game needs a referee with more experience."
Eriksson has been selected by FIFA to referee at the World Cup finals in Brazil this summer, and the world governing body's referees chief has already dismissed Pellegrini's comments.
"I read the remarks that were made by the Manchester City manager," said Jim Boyce, a FIFA vice-president from Northern Ireland.
"I saw the game and my own personal opinion is that I thought the referee had a good game. He is a very experienced referee who has been chosen for the World Cup because of excellent reports of his performances in Europe."
Demichelis was sent off for a foul on Lionel Messi when the Argentinian forward was through on goal.
Replays suggest the incident was just outside the box, but a penalty was awarded which Messi scored. Barca then grabbed a late, and potentially decisive, second late in the game through Dani Alves.
While his manager let rip in the post-match press conference, Demichelis has admitted he cannot blame Eriksson for awarding a penalty.
"I tackled him (Messi) because we were still outside the box," the veteran defender told The Sun.
"But I don't blame the referee. It happened all too fast. I have seen the moment again on TV and think 'why did I have to tackle him and not keep running by his side?'
"I was sure I would get the ball when I made the tackle. And then you think that you will steal the ball from Messi, you realise that you don't. But I made the foul."
City's slim hopes of progression have been further complicated after it was confirmed their FA Cup quarter-final against holders Wigan will kick off at 4pm on Sunday March 9, just three days ahead of the return leg at the Nou Camp.
Even programme host BT recognises its scheduling is tight for City, stating the game "will fall just days before... the crucial second leg" with the Spanish champions.
However, with interest high in what is a re-run of last year's final - won 1-0 by Wigan - they wanted the match for a prime-time slot.
City's run of cup games next month begins with the Capital One Cup final against Sunderland on Sunday, March 2.
Following a clash at home to Stoke this Saturday, City do not face another league game for three weeks as their cup commitments kick in.