Ji-Sung Park has warned United to not be complacent
United are level with Manchester City at the top of the table on 19 points – five points ahead of third-placed Tottenham.
Both sides have started the season in unstoppable form, winning six and drawing one of their opening seven matches.
However, Park, who won four Premier League titles during a seven-year spell at Old Trafford, has fired a warning to Jose Mourinho to not rule out Chelsea, Arsenal or Tottenham from clawing back the deficit.
"I know this moment, it's two clubs that really fight each other, but the season's long,” the South Korean told CNN Sport.
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The season's long, just focus on what they [United] have done because they've done so well and if we can continue with that then I think we can win the title again.
Ji-Sung Park speaking about United's title chances
“I know Chelsea, Arsenal and Liverpool all compete during the season.
"Always the Premier League has several clubs fighting for the title.
"At the moment, it looks like two clubs. We need to show our quality and don't think about other clubs, like Man City.
"The season's long, just focus on what they [United] have done because they've done so well and if we can continue with that then I think we can win the title again."
Park won four Premier League titles while at United
United have not won a title since Sir Alex Ferguson retired in 2013.
But Park believes the glory years are about to return under the guidance of the Mourinho.
"We're almost through that dark tunnel," Park said.
"After Sir Alex Ferguson it's been a difficult time for Man United, but actually many people know that after Sir Alex Ferguson it would be difficult time for Man United.
Park believes Jose Mourinho can turn United into a great team once again
“Now you can see this season, the performance is great. Hopefully it will be the same as under Sir Alex Ferguson."
"Particularly this season, they are doing so well under Mourinho. He knows more about Man United now.
"His second season is always good. In his first season, he knows what the club wanted. He found some things, brought in some players who he wanted and now it looks strong."