After an impressive start to his tenure as Manchester United manager that has seen him win each of his first four games in charge, Jose Mourinho faces his biggest test of his young Old Trafford career this weekend.
In just five days time, United will put their 100 percent record on the line in the Manchester derby against a Man City team who also boast three wins from three in the Premier League this season.
Facing such a challenge, the Portuguese will need his best squad available if he is to out manoeuvre Pep Guardiola and co.. With that in mind, he will be delighted with news coming out of Belgium today.
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That's because, according to Kristof Terreur - a journalist for Belgian newspaper HLN - Marouane Fellaini has been given a clean bill of health just over one week after suffering a back injury in United's last-gasp win over Hull City.
It had been widely thought that the Belgian midfielder would be unavailable for the Manchester derby after he picked up what was described at the time as a "bad" injury in his last outing for the Red Devils.
Although he travelled with Belgium for their friendly against Spain this weekend, the fact Fellaini didn't play a part in the game added to the theory he'd be out of action this weekend.
Today's news, though, is a huge boost for Mourinho as he prepares his side for the visit of City on Saturday afternoon.
After impressing in an unlikely starting role in the early stages of the season, Fellaini's absence would have meant the United manager reshuffling his starting lineup for what is already being described as a crunch Premier League fixture.
However, it now looks like the 28-year-old will be able to continue his flourishing partnership with Paul Pogba in the centre of the Old Trafford club's midfield.
Just a few months ago, had anyone suggested United's hopes of getting a result over their cross-town rivals would be influenced by the availability of Fellaini they'd have been laughed out of Manchester.
Having slotted into the defensive midfield role so well under Mourinho, though, he is now seen as the perfect foil to the more attack minded Pogba.
He certainly offers more protection to the back four than the likes of Ander Herrera and more mobility than Michael Carrick.
With Morgan Schneiderlin struggling to convince Mourinho of his value so far this year, Fellaini's recovery from his back injury comes at the perfect time.
City have started the season just as quickly as United and, with the likes of Kevin De Bruyne, Nolito and David Silva in fine form, Fellaini will certainly be in for a tough 90 minutes show he be enough to start this weekend.