Manchester United are well aware that they still need a world-class defender to compete for the titles they want. According to The Mirror, the British club will go after Raphaël Varane next summer. Considering how badly the De Gea transfer saga ended, it would be very surprising to see Real Madrid accepting a Manchester United-offer for Varane.
The French defender has been a starter for Real Madrid since the season started. Pepe had some physical problems so maybe that's why Benítez gave Varane the chance, but the French defender has performed very well and it would be somewhat unfair to bench him. Varane is 22 years old and he has matured enough to become a starter for Real Madrid this season, but Pepe is also one of the leaders of this team and it would be shocking to see him on the bench more often than not.
Still, it's highly unlikely that Madrid will sell Varane to United any time soon.