Sergio Aguero is believed to be contemplating leaving Manchester City at the end of the season.

The Daily Express is reporting that City sources have said the Argentine striker is unhappy with the treatment he has received from manager Pep Guardiola of late.

Aguero was left out of Wednesday night's Champions League clash with Barcelona which City lost 4-0 at the Nou Camp and it is understood that despite publicly copping the omission on the chin, the star striker was fuming behind closed doors.

The 28-year-old has two years remaining on his current City contract but is now having second thoughts about penning a long-term deal as tension between he and Guardiola grow.

Aguero, who has nine goals in 11 outings this season, was also on the bench for the Premier League meeting with Everton on the weekend.

Guardiola's treatment of key City squad members like Joe Hart (loaned to Torino), Samir Nasri (loaned to Sevilla) and Yaya Toure (left out of Champions League squad) has now been extended to Aguero who may exit the Etihad Stadium at season's end, which is sure to alert big clubs in Europe, including some top Premier League sides and German champions Bayern Munich.

The fact Brazilian young gun Gabriel Jesus will arrive in January, providing further competition to Aguero, could also prompt the former Atletico Madrid ace to pack his bags if things don't improve throughout the course of the campaign.

Guardiola is also believed to be monitoring Borussia Dortmund star Pierre-Emerick Aubameyang and Atletico's Antoine Griezmann.