The centre-back was questioned on his commitment by manager Jose Mourinho last season.
However, in his defence, Smalling points out that he pushed his body to the limit against Chelsea and he was equally disappointed to sit out of games with injuries last season.
The England international said: "You just keep playing until physically you can't, and that was the story with the break. I had a couple of injections because I wanted to play in the Chelsea game but soon after that it got worse and that's when I had to have the lay-off.
"You always want to push yourself because you don't want to let the fans down or the players because they're the ones you train with every day.
"I think in the Chelsea game I proved that I can play with injections. To be honest, I don't think any player is ever 100 per cent. There's always something. There are always going to be some niggles.
"As players, it's not about always being 100 per cent. It's about going on the pitch and doing a job. We're always managing things – that's why we have so many physios and stretches and whatever – but nobody is ever 100 per cent."