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Wayne Rooney's acolytes will try to insist otherwise but the biggest 'shock' about the Manchester United line-up against Leicester was the omission of Michael Carrick.

Faultless at Northampton and a specialist in the 4-3-3, Carrick saw a more attack-minded midfielder in Ander Herrera start ahead of him. The only previous occasion Herrera played as the holding midfielder was as a substitute against City, when he ran around like the Battery Bunny during a frantic second-half.

Paul Pogba received the Man of the Match award from the broadcasters and his club on Saturday yet it could easily have gone to Herrera. Yes, Leicester might be deprived of N'Golo Kante and Claudio Ranieri might regret leaving Shinji Okazaki on the bench, but their midfield caused United concern in the Community Shield and Danny Drinkwater is capable of releasing their pacy forwards.

"Herrera was really good going for the second balls," Pep Guardiola noted after the derby. Herrera relishes that yard dog role but also has the refined pedigree of a Crufts finalist. He's a midfield terrier.

Carrick was possibly United's poorest performer in the Community Shield and Mourinho might have been mindful of that, amid the justifiable clamour to start the 35-year-old. It was still a risk starting Herrera that deep. He is a forward-thinking midfielder who has convinced as a playmaker on occasion, and even during that industrious effort in the derby his positional play was occasionally indisciplined.

What sets Herrera apart from Carrick and Morgan Schneiderlin is his aggression. Carrick and Schneiderlin are placid players. Carrick's only United red card was for kicking the ball away in Milan six-and-a-half years ago and Schneiderlin collected just five yellow cards last season, which is a low amount for a defensive midfielder. Darren Fletcher, at his zenith between 2008-10, was sent off in each campaign and saw yellow flourished at him 13 times.

Herrera is - and this is a compliment - snide. Opposition supporters have noticed this and what was almost as valuable as Herrera's improvisational prod for Anthony Martial's FA Cup semi-final winner was his cynical tackle on Ross Barkley. It killed an Everton counter-attack and MUTV's Stewart Gardner joked with Herrera at the Player of the Year awards he should win Tackle of the Year.

Herrera's face lit up. "I know you like it! I had to do it!" He has already received 17 bookings at United.

Jose Mourinho likes a s**thouse in his midfield. Pepe and David Luiz both played there in intense encounters for Real Madrid and Chelsea. Costinha wound up United supporters for his play-acting almost as much for his celebration in that 2004 Champions League knockout tie. Don't be fooled by Claude Makelele's petite frame. He could be as antagonistic as his more voluble Chelsea teammates.

Herrera excels at s**thousery. He might have watched videos of United surrendering at Anfield before he headed to L4 last year, when he provoked Steven Gerrard into stamping on his shin. His performance that day was the best from a United midfielder at Liverpool since Roy Keane raged against the dying of the light in January 2005.

United have lacked aggression in the middle third for the majority of the 11 years they have coped without Keane. Football changed and Sir Alex Ferguson adapted, winning five more titles without his greatest captain, but the squad he left David Moyes was lightweight and the soft centre still required beefing up this summer.

Moyes and Louis van Gaal signed six central midfielders but Angel di Maria, Daley Blind and Schneiderlin were equable acquisitions. Bastian Schweinsteiger lacks durability. Marouane Fellaini's elbows have claimed just the one victim so far this term, but his immobility was bound to be inhibitive so deep at some stage.

It is early days, but Herrera has shades of Owen Hargreaves' assiduousness. Hargreaves brought a controlled aggression to the United midfield in 2007-08, breaking up attacks and setting the tempo without being intimidated, while also putting himself about.

Look again at the melee following Didier Drogba's slap on Nemanja Vidic during the 2008 Champions League final; it's Hargreaves who is in referee Lubos Michels' ear, effectively pushing him towards Drogba so he can dismiss the Chelsea striker.

Ferguson regarded Hargreaves as a 'disappointment' but his consistent excellence that season suggests otherwise and one of the main reasons behind United's failure to emulate the feats of their double-winning side is they never properly replaced Hargreaves.

Herrera has the capabilities to bring that constructive pugnacity to United's midfield. He runs like a Brownlees brother without collapsing and emerged from the conveyor belt of diminutive Spanish midfield maestros, with a Basque belligerence that makes him so suited to English football his nationality could be mistaken.

The issue is discipline. Herrera often strayed too far forward whenever Van Gaal started him in a deep midfield two, isolating his partner, and as United chased the game against City he could not resist haring forward, which enlivened Kevin de Bruyne and almost resulted in a clincher on the counter.

Mourinho is quick to single out players who do not run backwards as well as forwards. Eden Hazard bore the brunt of Chelsea's 2014 Champions League semi-final loss to Atletico Madrid and Gary Neville noticed Paul Pogba was foraging into his own third, as well as Leicester's.

"I don't think Mourinho will look at that performance and think Pogba and Herrera are his midfield two for Manchester City at home, or Liverpool away or Chelsea away," Neville justifiably observed of the Leicester win. "United have got three games in the next six that are against Chelsea, Liverpool and City.

"In those games Pogba and Herrera, if they are going to play together, can they then go and deliver in the bigger games and against the better opposition? When you've got Coutinho playing in the hole and pockets behind you, you've got Silva, De Bruyne, Hazard, Oscar and players like that. That's when the ultimate test will come."

Pogba is as certain a starter in this United side as David de Gea, unlike Herrera. The acid test awaits after the international fortnight, beginning at Anfield in the first nocturnal league encounter between English football's greatest rivals since 2004.

There'll be a shock if Herrera doesn't start that game.