The Portugal global flopped at the Nou Camp last season after arriving in the summer of 2016.
After a poor start to their league campaign, Hammers manager Slaven Bilic is desperately looking bolster his squad, and the Portuguese worldwide is apparently seen as a ideal fit.
Speaking to the press while on global duty, he said: "I was coming on against City and he (Bilic) said 'Where do you want to play, on the left or right?"
The right-back broke into the Bhoys side at the end of last season, and has been used four times in this campaign with his performances catching the eye of a number of sides, the Hammers included. I hate that position but when you are Scottish you are brought up to play anywhere.
England's transfer window will close at 11.00pm (midnight South Africa time) tonight, which means there is not much time left for West Ham to get this deal done.
West Ham finally play their first home match of the season when they return from the global break when they host Huddersfield Town at the London Stadium, but prior to that all eyes will be on Slaven Bilic to see if he does any last minute business before the window closes.
The Hammers were insistent all along that Sakho would not be sold but off his own back, the striker flew to France to complete a move to Rennes.
Speaking from Chelmsford, McKay said: "No bid has been accepted".