This weekend, Manchester United face their biggest game of the season so far when they welcome Manchester City to Old Trafford.
But, according to reports today, Jose Mourinho might have to go into the crunch fixture without two key players.
Per The Mirror, both Luke Shaw and Antonio Valencia are, for different reasons, considered a doubt for Saturday afternoon's Manchester derby.
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Shaw's status is unclear after the left-back returned early from England duty due to a calf issue picked up in training with the national side.
Valencia, meanwhile, could be hard-pressed to be ready for the lunchtime kick off this weekend because he won't return from his own international exploits with Ecuador until around mid-day on Friday.
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The prospect of being without both of his starting full-backs for the game against City will undoubtedly be causing Mourinho a few selection headaches with just five days to go until the crunch fixture.
With Shaw having only recently returned to first team action after recovering from the nasty double leg break he suffered last September, the Portuguese manager is unlikely to want to take unnecessary risks with the in-form England international.
As for Valencia, we've seen in the past instances where players have come back from far-flung international fixtures and appeared sluggish in their return to Premier League duty.
If Mourinho is forced to leave both full backs out of the starting line up on Saturday, it will mean some fairly major defensive reshuffling.
One option would be to move the versatile Daley Blind across to left-back in place of Shaw and insert Chris Smalling into the centre-back role vacated by the Dutchman.
However, that would mean splitting up a Blind-Eric Bailly partnership that has shown a lot of promise in the early weeks of the season.
As for replacing Valencia, Italian right-back Matteo Darmian would be the likely candidate, whilst Phil Jones could also step in. The issue there is that neither player has played a single minute of Premier League football this season.
Coming in to compete against a Manchester City attack that looked in ominous form before the international break would be a big ask, and one that could backfire on the Old Trafford club.
Whilst the Red Devils hierarchy puts together their defensive plan for the Manchester derby, they did receive more positive news on the injury front this morning regarding the fitness of Marouane Fellaini.
The Belgian midfielder was expected to miss this weekend's fixture with a back injury but is reportedly back to full fitness already.
With Sergio Aguero suspended for City, it is looking increasingly likely that Saturday's top of the table clash could be decided by the form of squad players, rather than big name starters.