Ronaldo was handed a rare start by Erik ten Hag but put in an uninspiring performance, as the Premier League side suffered a 1-0 loss at Old Trafford.
The 37-year-old was desperate to leave the club this summer and was absent from the club’s pre-season tour of Australia and Thailand.
He lost his place in the starting XI following the humiliating 4-0 defeat to Brentford in mid-August with Ten Hag picking a younger, more dynamic front three of Marcus Rashford and Jadon Sancho, with Antony or Anthony Elanga.
And former Liverpool right-back Nicol pointed the finger at Ronaldo after he wasted several chances in the defeat to La Liga side Real Sociedad on Thursday.
‘I’ll be honest, when you mention the game, the only thing I have in my head is Ronaldo clean through [on goal] and getting caught by two players, Nicol told ESPN FC.
‘That’s kind of what springs to my mind. And he did have another look.
‘He had a couple of other chances, not as good as that one, but there was just something missing.
‘That’s what I think about when I think of this game. There wasn’t much in it between the two sides, not that many chances in the game.
‘But that’s the only thing I can think of. The fact that Ronaldo was clean through and looked every one of those 36, 37 years.’
Ronaldo scored 24 times in 38 matches last term but United’s performances suffered following his arrival from Juventus.
United are going through somewhat of a purple patch in the Premier League since dropping Ronaldo to the bench, winning their last four top-flight games in a row, with Ten Hag’s side up to fifth in the table.