While Arsenal remain in pole position for the centre-back, the deal had not been finalised when the potential move to United emerged.
Lille center-back Gabriel Magalhaes has delayed the final decision on his future and expects Manchester United to make a late bid to land him with a £ 22.6million contract.
Arsenal led the race for the 22-year-old Brazilian and made a deal to move him to the Emirates Stadium, although Napoli have also targeted him and it is believed United will now make a dramatic gesture.
United coach Ole Gunnar Solskjaer is looking for a center-back for partner Harry Maguire at the heart of his defense next season and Gabriel has become a low-risk option for Premier League clubs given his asking price and his experience in the Champions League with Lille.
While Arsenal remain in pole position for Gabriel, the deal had not been finalized when the potential transfer to United emerged.
Solskjaer placed in the top four on the final day of the season and will play in the elite European competition next season.
Gabriel has been attracting interest from clubs since Ligue 1 was called off due to the coronavirus pandemic, with Everton being the first club to make a move and put a deal in place before competing for his signing.
Napoli have always been in contention for the player who arrived from Brazilian club Avai three years ago and had loans at Troyes and Dinamo Zagreb.
Arsenal were set to land him this week, but the delay means United can enter the race. Solskjaer made Maguire his captain at Old Trafford, but he wants competition from Victor Lindelof, who has teamed up with the England center-back for most of the season.
United also have Eric Bailly, Timothy Fosu-Mensah, Axel Tuanzebe but Marcos Rojo can leave for the fair price and Phil Jones has suffered injuries.