The Red Devils appeared to be in crisis mode following successive Premier League losses in August.
Manchester United lost 3-2 to Brighton before a humiliating 3-0 defeat by title rivals Tottenham Hotspur at Old Trafford.
However, the 20-time English champions bounced back with a 2-0 win at Burnley before the international break to end their losing run.
Smalling got on the score sheet to help Manchester United end Watford’s 100 per cent start to the season with a 2-1 victory at Vicarage Road.
Manchester United will switch their focus to the Champions League on Wednesday night ahead of their group-stage opener at Young Boys.
Smalling believes the Red Devils have made big improvements over the past couple of weeks and have put their poor start behind them.
“I think it has definitely come together in the last couple of games,” Smalling told Man United’s website.
“Obviously, Burnley was comfortable through the whole game; the first half [against Watford] was comfortable and the second was about digging in when we knew we weren’t always going to have it our own way, but all credit to all 11 players out there.”
Manchester United lost 1-0 to Basel in Switzerland in last season’s Champions League group stage to offer Young Boys belief of a potential upset.
The Red Devils haven’t won the Champions League title since 2008 when Sir Alex Ferguson’s side beat Chelsea FC on penalties.
Manchester United lost to FC Barcelona in the Champions League final in 2009 and 2011.
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