The Old Trafford board have told Jose Mourinho to offload players if he wants to add to his squad in January as a means to control costs.
Mourinho has spent £285m on transfer fees on six major signings during his two years at the club.
United’s most recent financial results, released in September, showed their wage bill had risen by 13.5% to £263.5m.
Defender Luke Shaw, who cost United £27m in 2014 but yet to start this season, is the most likely departure.
The 22-year-old has started just four Premier League games in 12 months through a combination of injury and poor form.
The future of Marouane Fellaini is also unclear. The Belgium midfielder’s contract expires in the summer and he will be free to negotiate with overseas clubs in January.
Sixteen first-team squad members have left since Mourinho took charge in May 2016, but only the £16m sale of Memphis Depay and the £22m departure of Morgan Schneiderlin generated significant income, while high-earners Wayne Rooney and Bastian Schweinsteiger have also left.
Sunday’s Premier League defeat at Chelsea left United eight points behind leaders Manchester City.