United announced on Friday that they had completed their £73m move for the highly rated 21-year-old English winger, who signed on a five-year deal.
The Red Devils are expected to continue strengthening their squad in the window, with Real Madrid star Raphael Varane heavily linked with a move to Old Trafford.
However, Sancho's arrival at United could mark the end of Martial's hit-and-miss spell at the Red Devils.
Martial, 25, has struggled to maintain himself as a regular starter under United manager Ole Gunnar Solskjaer.
The France international, who was signed by United in 2015, now faces even tougher competition in the first team against the likes of Sancho.
According to The Daily Star, United are reportedly willing to axe Martial in the bid of recouping some of the money spent on Sancho's hefty transfer fee.
But Martial's departure from Old Trafford could prove tricky, with United valuing the Frenchman at a £50m transfer fee.
Tottenham are interested in the United forward, but the Premier League club would have to splash out to match his £250,000-a-week wages at the Red Devils.
The Daily Star reports that Spurs chairman Daniel Levy isn't open to making Martial one of the top earners at the club.
Tottenham are keen to reinforce their attacking options amid uncertainty over the future of Harry Kane, who has been linked with a £160m British transfer record move to Manchester City.
Former United manager Louis van Gaal was in charge at Old Trafford when the Red Devils splashed out an initial £36m to sign Martial from Monaco.
Martial has scored 78 times in 258 appearances for United, with the ex-Monaco star often criticised for his finishing in the final third.
He missed the end of United's season after he suffered a ruptured knee ligament injury during international duty with France in March.
Featured Image Credit: PA/Manchester United
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