While the 6-1 defeat by City was a collective disaster, Smalling has yet to hit the wall as an individual in United's colours.
But he's prepared for that challenge should it arise.
"Everybody's career is not plain sailing. I have been very much enjoying how it has gone over the last couple of years and hopefully it will stay on course," he told the Manchester Evening News. "But I will be ready if there is a setback and I will work hard.
"When I was younger I stopped playing for a professional club after being at Millwall's Academy. I was at school and I thought the chance in the pro game might not come again. But I was always going to give it a go and keep at it and worked hard. I never gave up and the reminder of that will always help me in the future. That will be the same response if I get a setback in the professional game. I learned from that.
"You cannot take anything for granted."