The Blades are believed to be one of two clubs vying for the signature of Club America’s £12m-rated Colombian forward Roger Martinez.
MSN in Mexico state that Club America technical director Miguel Herrera has admitted there are two clubs in the race to sign the 25-year-old.
Other South American media reports claim one is an English team that has already made the first approach to the Mexican outfit over a deal – and that club is believed to be Sheffield United.
Martinez impressed for Colombia at the recent Copa America and Club America will push for a £12million fee if he expresses his desire to leave the club.
He has been something of a football nomad already in his career with spells passing through Boca Juniors, Racing Club, Ramon Santamarina, Aldosivi, Racing (again), Jiangsu Suning and Villarreal before he landed in Mexico.