The Portugal forward missed United's pre-season tour to Thailand and Australia because of personal reasons amid speculation over whether he would be leaving Old Trafford.
It has been reported Ronaldo wants to play Champions League football, but United maintain the 37-year-old is not for sale and remains an integral part of the plans of new boss Erik ten Hag.
Ronaldo played the full 90 minutes of United's 4-0 defeat at Brentford on Saturday, which left them bottom of the Premier League.
In a reply to a fan account on Instagram which referred to a report linking the United frontman to Atletico Madrid, Ronaldo said: "They (will) know the truth when they interview in a couple weeks. The media is telling lies.
"I have a notebook and in the last few months of the 100 news I made, only five were right. Imagine how it is. Stick with that tip."
Manchester United will look to kickstart their Premier League campaign when they host Liverpool on Monday night.
United's owners have come under fire following the team's terrible start, with former defender Gary Neville warning the club could finish in the bottom half of the Premier League if they do not address their "horror story" recruitment strategy.
Billionaire Elon Musk, meanwhile, sparked a social media frenzy when he teased the prospect of buying United from the Glazer family.
The Tesla founder made the comment in a late-night tweet, then later clarified his position by saying he had no intention of buying a sports team and that it had been a "long-running joke".
His post quickly garnered a lot of attention, receiving more than 36,000 retweets and almost 200,000 likes within a couple of hours.
But, responding to Tesla owners asking if he was serious, Musk tweeted in reply: "No, this is a long-running joke on Twitter. I'm not buying any sports teams."
United have been owned by the Florida-based Glazer family since 2005.
Their ownership has regularly come under fire from fans due to the debt, dividends and mismanagement that followed their controversial takeover.
The Glazers have also overseen a sharp decline in performances and results in recent years.
The record 20-time champions of England have not won a Premier League title since Sir Alex Ferguson's final season in charge in 2012-13 and no kind of silverware for five years.