Sunderland are said to have lodged an £11 million bid for Sakho last month but with little movement since, the Senegalese has reportedly handed in a transfer request.
Their failure to make a breakthrough the likely factor holding up Sakho's exit, however, Sunderland boss Sam Allardyce appears to be losing patience.
The 61-year-old has recruited heavily from France, historically, adding Wahbi Khazri and Moukandjo's former teammate Lamine Kone in January, and oversaw Sakho's arrival at Upton Park two summers ago.
Moukandjo, who was initially linked with the Mackems in April (Daily Mail), scored 13 goals for the Ligue 1 side last season and was previously valued around the £8 million mark.
Sunderland, who are awaiting their first summer signing, were linked with a shock move for former Newcastle right-back Davide Santon on Thursday (Mail).