The Red Devils are close to signing Varane from Real Madrid and he's regarded as one of the world's top defenders.
Despite winning four Champions League titles and the World Cup, Danny Mills has questioned if the 28-year-old is the 'right signing' at Old Trafford.
He told talkSPORT: "If all those other teams are getting stronger, they are more likely to take points off Manchester United as well.
"Their away record, Manchester United, was superb as well and I don't think that is going to be the same, especially with fans back in and everything else that is happening.
"Yes he's [Varane] a good signing, but was he the right signing?
"Varane is a good player, but again we don't know what he is going to be like and how robust he is going to be in the Premier League week in, week out.
"He's used to playing eight-ish tough games a season, plus the Champions League.
"Him and [Sergio] Ramos could get through games at Real Madrid with a cigar on. You can't do that in the Premier League.
"Every single foreign player who comes, [Kai] Havertz and [Timo] Werner said it, 'we didn't realise the intensity of every single game'."
Varane is set to cost United around £50 million and they've chased his signature for some time.
He is ready for a new challenge after a decade in Spain and underwhelming season with 'Los Blancos'.
The former Lens man is entering the final year of his deal and Madrid have already seen Sergio Ramos join Paris Saint-Germain on a free transfer.
United manager Ole Gunnar Solskjaer was asked about transfers following Sunday's 2-1 win over Derby County.
Jadon Sancho is set to be confirmed as United's second signing of the summer after Tom Heaton, but Solskjaer kept his cards close to his chest.
The Norwegian coach told Sky Sports: "There are a couple of things to do with paperwork but we hope we can announce one player who has had a lot written about him. We are working, we want to have a strong squad.
"I don't think it's a secret we have a deal with Dortmund, but until the paperwork is done he is still a Dortmund player."
When asked about Varane, he replied: "Same again."
Featured Image Credit: PA Images
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