The 29-year-old has been under-fire for United this season, having not started for them in the Premier League since their 4-0 defeat to Brentford last month, but said he deserved his place in England's starting lineup after their loss to Italy.
"On my form, I don't know what has been said, I don't really read about it," Maguire told talkSPORT.
"I am working hard on the training pitch to make sure I am ready for when my opportunity comes. That is all what I can do to try and help the team.
"I am not concentrating on anybody else and what people are saying, I think if people can make a story about me, I am Manchester United captain, it is going to make big news.
"So that is the reason they do it, they like the clicks and things like that, but I went into the Euros after an eight-week injury, and did not play one game, and got into the team of the tournament.
"In terms of rustiness, and things like that, I am sure that won't happen."
Maguire also asked England supporters to show their backing ahead of the World Cup, with Southgate's team winless in their last five matches and having failed to score in their last three games.
"We're a strong group mentally -- we've given people an unbelievable five years or so," Maguire told the BBC. "We're in a period where we have to come together.
"The fans are probably frustrated and they have to stick with us because we've got a big tournament coming up.
"To win that tournament or progress in that tournament, we need the fans with us, so whatever has happened in recent months we are working tirelessly hard to improve that and get back on track, because it is a big winter and World Cup and we need to make sure we're ready. And we will be."
Information from Reuters contributed to this report.