According to Sam Lee of Goal, the forward is "discontent with life under Pep Guardiola" and "it took a personal intervention from Blues chairman Khaldoon Al Mubarak to resolve the same issue earlier this year."
It's suggested in the report the Argentina international feels as though he has been "treated unfairly" by his manager and that Guardiola "will ultimately force him out of the club."
Lee reported that Aguero was unhappy earlier in the campaign when Guardiola turned to Gabriel Jesus to lead the line instead of him and ended up speaking with Al Mubarak in Los Angeles in the summer about his future.
Transfer talk was reportedly quelled as a result, but "in recent weeks he has come to the conclusion that things have not changed." Aguero was left on the bench in place of Jesus for City's 2-1 win against rivals Manchester United.
Earlier in the campaign, Guardiola did seek to pair Aguero and Jesus, although as the season has rumbled on it's become clear that the manager prefers one or the other.
Bleacher Report's Sam Tighe suggested that using a sole striker is suited to the way Guardiola wants to play:
As noted by Tom Williams of Agence France-Presse, there were signs of unhappiness from the City No. 10 in the 4-1 win against Tottenham Hotspur, when he was withdrawn for Jesus:
Despite missing some fixtures, Aguero has still enjoyed a memorable campaign, with 13 goals scored already. Additionally, he became the club's all-time top scorer with a strike against Napoli, taking him on to 178 goals since his arrival in 2011.
Nevertheless, Guardiola has proved to place emphasis on the team as a whole, and when Jesus does start at the top end of the pitch, City are just as effective.
While the Brazilian is not as potent in front of goal as his team-mate, his energy, movement and linkup play brings others into play. In big games Jesus started away from home, most notably at United and Chelsea, City have been excellent.
As Goal UK noted here, Jesus has been something of a lucky charm for City when he has started matches:
Goal UK @GoalUK
Gabriel Jesus hasn’t lost any of the 26 Premier League games that he’s played in since joining Manchester City – only four players have ever had a longer unbeaten start to a Premier League career (Jens Lehmann 47, Arjen Robben 37, Didier Drogba 37 and Gael Clichy 29). https://t.co/j0A5TajRbt
Having been the main man up top for City for so long, Aguero may be a little miffed at having a genuine challenger for his starting spot. Yet with City 11 points clear at the top of the Premier League table, into the UEFA Champions League knockout stages and the semi-final of the Carabao Cup, there's little to argue about.
Aguero remains one of the game's most dangerous forwards and will have ample opportunities to make his case for regular starts. But if Jesus continues to get the nod in the showpiece fixtures, the more senior striker may have a big decision to make in the summer.