The Spain international is widely seen as one of the very best players in his position, but rumours indicate that the Catalan club are willing to sell for the right price.
This has alerted the Manchester duo, who are both keen to recruit the 25-year-old.
United have already signed two left-sided defenders in the shape of Marcos Rojo and Luke Shaw during Louis van Gaal’s tenure, but the Dutchman is understood to remain keen on landing another option in the position.
City boss Manuel Pellegrini is also interested, and has reportedly asked the club’s hierarchy to make funds available for a move.
However, Barca are unlikely to sanction a move unless a replacement can be found, which could scupper any January efforts for Alba given a lack of top class options being available.
The rampaging defender has been a key member of the first-team at the Camp Nou since his arrival from Valencia, and also helped Spain to European Championship glory in 2012.
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