Lisandro Martinez's frustration with United's transfer business boiled over on Tuesday night as he launched an attack on their transfer dealings.
The flashpoint reignites particular questions over their decision not to sign Hall.
The left-back area remains a big problem for United, where doubts over Luke Shaw's ability to remain fit for a full campaign were already well established before the season began.
Those concerns have resurfaced, with Shaw unavailable for key games already this term, forcing the club to rearrange personnel to cover the position.
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Martinez has hit out at United's hierarchy for failing to invest more heavily in the squad - and Hall was United's leading target for the left-back role during the summer.
Newcastle did not want to entertain offers for the England international and United ultimately backed away. But at the time, United had reason to believe the player was interested in the move and a valuation of around €70 million (£59.1m) was mooted.
A deal never advanced and Hall has since committed his future to Newcastle by signing a contract extension that runs until the summer of 2031.
Such a moment strengthens Newcastle's negotiating position and makes any potential departure even more difficult.
Flashscore reported last month that a move for Hall next year could cost United more than it would have done during the previous transfer window. There is growing talk of Newcastle's valuation potentially exceeding €100 million (£84.5m) as the defender's standing in the game continues to rise.
United remain admirers of Hall and would like to revisit the possibility of signing him, but the financial demands are a major obstacle.
Their poor start to this season means funds may become even more limited for 2027 as they may not qualify for the Champions League.