McNair was injured in Northern Ireland's final Euro 2016 qualifier, a 1-1 draw against Finland, coming off early in the second half.
The 20-year-old, making just his second competitive international start, suffered bruised ribs and an abdominal injury while there were also concerns he might have damaged his liver.
While his team-mates flew home following on Monday, McNair was kept in hospital for assessment for two further nights with Irish FA doctor David White in attendance.
He was allowed to fly back to Manchester on Wednesday but is expected to face at least another fortnight on the sidelines.
Source : PA
Source: PA