8:44AM BST 20 Sep 2012
Nasri limped out of the 3-2 Champions League defeat at the Bernabeu shortly before half-time after pulling up while clutching his right hamstring.
The France international is already set to miss Sunday's clash against former club Arsenal at the Etihad Stadium.
While Nasri fears a lengthier lay-off, his immediate signal to the bench that he had suffered the injury may yet have spared him more extensive damage.
City are set to assess the full extent of the injury in the next 24 hours, however, after scanning the injured hamstring.
Meanwhile, Nasri's team-mate Gareth Barry feels the club can take much pride from Tuesday's defeat which came in the 90th minute when Cristiano Ronaldo scored the winner for Jose Mourinho's side who twice came from behind before clinching victory.
Marcelo and Karim Benzema also scored for Real in a dramatic fightback after Aleksandar Kolarov looked to have snatched an unlikely City win six minutes from time.
That late drama came at the end of a remarkable 22-minute period in which all five goals were scored, Edin Dzeko first putting City ahead against the run of play.
Barry said: "We knew they were going to have the ball for long periods.
"We didn't set out to frustrate them but we set out to work hard and hit them on the counter-attack. As we showed throughout the game we are pretty dangerous.
"Yaya (Toure) had a great chance and if that goes in it is 2-0 and a different game.
"We played a good game and there are a lot of positives but overall we are disappointed.
"Playing away is always tough in the Champions League. To have got so close to the three points is disappointing but there is great stuff we can take from it."
