Sergio Aguero stretchered off while playing for Argentina

The 27-year-old, fresh from plundering five goals in City's 6-1 Premier League win over Newcastle last Saturday, was carried off on a stretcher after sustaining the problem to his left leg midway through the first half in Buenos Aires.

Aguero is set for a scan on the injury and has been ruled out of Argentina's next game with Paraguay next week.

Coach Gerardo Martino said the injury to his left leg meant he would not make the game in Asuncion.

"Aguero had a problem from his last game with City, where he played well for 65 minutes," Martino told reporters after the match.

"We looked after him this week, he was moving well, very comfortable, but he felt the strain and unfortunately we are going to lose him."

Aguero's injury was just the start of the bad news for Argentina: two goals in two minutes gave Ecuador a shock 2-0 win in Buenos Aires - Argentina's first home defeat in six years - as the Andean side got off to a flying start in their bid to reach the 2018 World Cup finals in Russia.

Frickson Erazo headed home the first goal after 80 minutes and Felipe Caicedo doubled their lead when he finished off a quick counter attack just a minute later.

Ecuador, who have qualified for the finals on just three occasions, troubled Argentina out wide the entire game and the home side could not impose themselves on a team 30 places below them in the FIFA rankings.

Manchester City confirmed Aguero's injury on their website, with a statement that read: "Sergio Aguero lasted just 22 minutes of Argentina's opening World Cup qualifier against Ecuador.

"The City striker, who scored five goals in his last game against Newcastle, pulled up holding his left hamstring while chasing a long ball downfield.

"Former Blue Carlos Tevez replaced Kun who was stretchered off after receiving treatment with the game at 0-0."

Aguero, who has only just returned to fitness after a knee injury earlier in the season, must now be considered doubtful for when City resume their Premier League campaign against Bournemouth on October 17.

This is very sad news indeed for Aguero and Manchester City. Every year it seems he picks up a significant injury just as he's hitting his stride - and for this to happen just a few days after his five goals at the weekend revitalised City's flagging campaign is the cruellest of blows.