Sergio Aguero has grown unhappy with life at Manchester City under Pep Guardiola

The Argentine could be on his way out in the summer.

Doubt has been cast over Sergio Aguero's long-term future at Manchester City after reports on Friday detailed the striker's growing frustration playing under Pep Guardiola. Aguero's relationship with Guardiola was scrutinised last season when City's all-time top-scorer lost his place to Gabriel Jesus following the Brazilian's arrival in January. Aguero only returned to the starting line-up after Jesus broke a metatarsal, ruling him out for two months. Aguero was convinced to stay at the Etihad Stadium in the summer by Khaldoon Al-Mubarak, the club's chairman, during a conversation held in Los Angeles on City's pre-season tour of the USA. However, according to The Times, the 29-year-old has become increasingly disgruntled after Guardiola dropped him for some of City's biggest matches in recent weeks. Although Aguero started the 4-1 victory over Tottenham last week, he was subbed off after 58 minutes and was an unused substitute in the Manchester derby. There is no indication that Aguero wants to leave City in January though. The striker has been settled in Manchester for years now and the player hopes that his relationship with Guardiola improves, but Aguero does feel as though his efforts to adapt his game to suit Guardiola's style have not been fully appreciated. The official line coming from the Guardiola camp, however, is that he has no problem whatsoever with Aguero, who has scored 13 goals in 19 appearances this season. He also surpassed Eric Brook as the club's leading scorer when he found the net for a 178th time in blue against Napoli. Aguero still has two-and-a-half years to run on his contract and, while City are under no pressure to sell, Real Madrid have always held an interest in him. City remain interested in Arsenal forward Alexis Sanchez. Although Guardiola has postponed plans to pursue the Chilean until the summer, it's possible that his arrival would prompt Aguero's departure. It's a tough one for City fans. Aguero is a hero to the club's fans and while it would be painful to watch him leave, the fact is that he is not as devastating as he once was. Some of Aguero's performances have been poor, which has left him susceptible to being dropped, unlike David Silva, Kevin De Bruyne and Raheem Sterling, all of whom have been consistently outstanding. There is a sense that Guardiola sees Jesus, a hard-working and selfless striker who possesses a clinical streak and gives City's attack a wonderful fluidity when he plays, as more fitting in the current set-up. It is starting to feel as though Aguero's time at City is slowly but surely coming to an end.