Ferguson was caught on camera questioning Solskjaer’s decision to leave Ronaldo on the bench for their 1-1 draw with Everton last weekend.
When Ferguson, who still refers to as “the gaffer” starts to doubt your judgment, you know you are heading towards trouble.
Between the Scot and Norwegian, United have appointed David Moyes, Louis van Gaal and Jose Mourinho.
All three coaches have found the Old Trafford job impossible to conquer.
After this international break, Solskjaer faces 10 games in 46 days.
These fixtures will surely determine his future, despite the lucrative new three-year contract he just signed in the summer.
United will play Liverpool, Manchester City and Chelsea, as well as tricky encounters against Leicester, Tottenham, Watford and a resurgent Arsenal.
They also face a double-header against Atalanta and a tough trip to Villarreal in the Champions League.
Despite the seeming progress he has enjoyed in his first two full seasons in charge, finishing third and second, Solskjaer acknowledged last week that he is in “a results business” and it is on that basis he will ultimately be judged.