Manchester United stunned the world last month when they signed Sanchez from Arsenal in a deal that also saw them manage to offload Henrikh Mkhitaryan.
However, the Chile international has experienced a rough start to life at Old Trafford, scoring once from four outings and toiling in defeats against
His arrival has also had a negative impact on Martial, who is reportedly weighing up his future at the club.
And SportsKeeda say Manchester United are worried about the impact Sanchez playing on the left has had on his French team-mate.
Both players prefer to play on the left than the right.
And that represents a huge problem for Mourinho, who now faces a fight to keep both players happy.
Sanchez started on the right in Sunday’s 1-0 loss to Newcastle but was shunted back to the left with Martial toiling.
And the Frenchman also struggled when he swapped positions, cutting a frustrated figure as the game slipped away.
SportsKeeda claim Mourinho has decided that Sanchez would be best-utilised on the left.
Yet he knows that would damage his relationship with Martial, who has shown signs of his potential this season.
Meanwhile, Arsenal ace Hector Bellerin has opened up on how Sanchez fell out with members of the squad during the closing stages of his time in north London.
“Alexis is an amazing player,” Bellerin told the Oxford Union.
“One of the best in the Premier League for sure but he is a player who always wants to win.
“He demands from everyone, sometimes it can be too much.
“The great thing is he wants to win, to give 100 per cent.”