Manchester City, Real Madrid, Bayern Munich and Paris Saint-Germain are also interested in Haaland, who can trigger a release clause in his Borussia Dortmund contract at the end of this season that is reportedly set at €75 million.
But although the deal to sign Ronaldo was financed outside of United's original summer transfer budget, sources have told ESPN it will not impact next year's recruitment plans and the ongoing effort to win the race for Haaland.
United will pay an initial €15m for Ronaldo with a further €8m in additional payments over five years, but while the transfer fee is relatively small, the Old Trafford club have had to make the 36-year-old the highest-paid player in Ole Gunnar Solskjaer's squad by some distance, even though sources have said he has taken a substantial cut on his Juventus salary, which amounted to £510,000 per week after tax.
Sources added that the opportunity to re-sign Ronaldo, who left United for Madrid in an £80m transfer in 2009, was one the club could not pass up, especially when it became clear that the Portugal captain was in talks over a move to neighbours City.
And while the deal has left United with an abundance of attacking options, the long-term objective of signing Haaland has not changed.
United came close to signing the Norway international from FC Salzburg during the 2019-20 winter transfer window, only for the player to opt for a move to Dortmund.
But although that failure resulted in United sources citing demands from the Haaland camp for a release clause as the reason their deal broke down, contact has been maintained with Haaland's representatives and Solskjaer's relationship with Haaland has also been unaffected. (Haaland played for Solskjaer when he made his senior debut as a teenager for the Norwegian team Molde.)
United expect stiff competition to sign the player next summer, with City's failure to sign Harry Kane from Tottenham last month increasing the likelihood of a sustained attempt by the Premier League champions to land Haaland.
Bayern regard Haaland as the ideal long-term replacement for Robert Lewandowski, and sources have said that PSG are prepared to move for the player to compensate for Kylian Mbappe's expected move to Madrid as a free agent at the end of the season.
Madrid, meanwhile, will also be in the race having avoided having to pay a transfer fee for Mbappe, whose contract at PSG expires in June 2022.
But United believe they have the resources to win the race for Haaland and that the arrival of Ronaldo could also strengthen their hand, with Haaland's admiration for United's new signing well known.