The defender suffered a groin injury at the end of last season which forced him to miss the European Championships, while a broken metatarsal in July delayed his return further.
Smalling finally made it back in action at the start of November and the 23-year-old says he is feeling stronger with every game.
“I feel good,” he told ManUtd.com and PA Sport. “I’ve been able to play a few games now and it’s just a case of keeping that going. The more games you have the more you get into a rhythm and the more confident you feel. I just want to stay injury-free now and hopefully go on a good run [of playing games]; there are lots of important matches coming up.
“It’s been one of the worst [injury setbacks] I’ve had. It started at the end of last season and then I missed the start of this season. It’s never easy to miss the start of the season and then come back into it, but I’m fortunate that I’ve started to get back into the team.
“The main thing you focus on when you get back is getting into a rhythm. You’ve missed out while everyone has been playing and doing well so it makes you focus harder to get yourself back to being better than you were before.”
Smalling says he has watched on with admiration as the Reds have comfortably qualified for the knock-out stages in the Champions League and taken control in the Barclays Premier League.
“It’s exciting to come back into the team particularly when you look at options we’ve got,” added the England international.