The 27-year-old did not make the cut for the Three Lions' recent friendlies against Germany and Brazil, Southgate citing concerns over Smalling's passing ability.
"I don't feel like I really need to prove anything to Gareth because I play under one of the biggest and most successful managers in Jose and he's only going to pick the best players," Smalling told Sky Sports News.
"While I'm playing regularly and he is happy I think ultimately if my season carries on like this and we have a successful season and our team still concedes very few goals, then I think it gives him maybe no choice in the summer but to pick me.
"I've been getting a good run of games over these last few months and I'm feeling good and that's the feeling you want, you want to be able to play regular games and be a part of a successful team. So far we have been successful, it's just making sure we keep this going and improve on last year where we got two trophies and we want to at least beat that."
Smalling has made 14 appearances for United so far this season.