The England international midfielder could be out of action for as long as two months if he is shown to have suffered a break or damaged his metatarsal in training last week
The England international is being sent for scans on Monday morning amid concerns the midfielder has broken his toe or damaged his metatarsal.
If the injury is confirmed, the former Aston Villa man could be out of action for as long as eight weeks.
"The medical staff at City are concerned that it's either a fracture or metatarsal damage which could keep him out for a couple of months if he doesn't get the all clear," a source close to the club told Goal.com.
Milner has not played a full 90 minutes for the Premier League champion so far this season, appearing only twice in the 2-2 draw with Liverpool at the end of August and City's win over QPR the following week.
The midfielder was an unused substitute at the Santiago Bernabeu as Madrid drew with Real Madrid last Tuesday and picked up the knock to his toe ahead of Sunday's draw with Arsenal.
The 26-year-old made only 17 Premier League starts as City secured its first title in 44 years last term, but his potential absence could leave Mancini short of midfielders comfortable playing on the left side of midfield, with Samir Nasri still recovering from a hamstring strain.
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