Vincent Kompany faces as big a fight to prove he can fit Pep Guardiola's prototype of a centre-half as he does trying to convince the Manchester City manager that he can win his long-standing fitness battle.
The City captain honoured his commitment to the club's medical staff to be more honest about his body after a plethora of injury woes by telling Guardiola that he was too "tired" and "not ready" to turn out for the second half of their 1-0 EFL Cup fourth-round defeat by Manchester United on Wednesday.
Guardiola has stated publicly that, to form part of his longer-term plans, Kompany must get and stay fit, but the defender faces a separate challenge to prove he can adapt sufficiently to the manager's insistence on playing out from the back amid concerns about his qualities on the ball.
The City manager cut an exasperated figure on the touchline at Old Trafford when he watched Kompany kicking the ball long on occasions and attempting to play overly adventurous passes that failed to reach their intended targets.
But while there is a recognition that Kompany has had a lot less time to adapt to a new way of playing under Guardiola as a result of the injuries that have restricted him to just 214 minutes of football this term, the Belgium defender is under pressure to conform to what the manager wants from his centre-halves.
There was also a feeling that, in the 1-1 draw at home to Southampton on Sunday, Kompany could have done more from a positional viewpoint to assist John Stones moments before the England defender played a blind pass in behind his team-mate that was pounced upon by Nathan Redmond to open the scoring.
Guardiola has wasted no time ousting some of the most influential figures in City's dressing room since he took charge in July and, in the process, axing the spine of the team that won two Premier League titles.
Goalkeeper Joe Hart and midfielder Samir Nasri were dispatched on loan to Torino and Sevilla respectively and Yaya Toure has been told he will not play for the club again unless his agent, Dimitri Seluk, apologises for saying Guardiola "humiliated" the Ivory Coast midfielder by omitting him from City's 25-man Champions League squad.
Guardiola has been determined to impose his own will and personality on the dressing room and if Kompany is not to suffer a similar fate to Hart and the others, the 30-year-old is likely to have to make a number of adjustments and improvements to his game in addition to regaining his long-term fitness.
Guardiola insisted last week that Kompany was part of his future plans and is respectful of the player's services to the club and the esteem with which he is held by supporters, but he also spoke glowingly about Hart, Nasri and Toure only to subsequently exile the trio.
Guardiola had wanted to sign two centre-halves in the summer, not just Stones, but Aymeric Laporte rejected an offer to join City to stay at Athletic Bilbao. Leonardo Bonucci was also heavily linked but Juventus were asking for too much money for the Italy defender. However, Guardiola will move for another centre-half next summer, as well as two new full-backs, a scenario that will place Kompany's future under even greater scrutiny.
Sergio Aguero's position has also come under the spotlight after he was omitted from the starting line-up for last week's 4-0 defeat at Barcelona. Guardiola recognises Aguero's quality and wants him on board, with City expected to announce in the coming weeks that the Argentina striker has signed a new contract. But there has been concern that Aguero's incessant pressurising of opposition defenders may have dropped as a result of the number of injuries he has suffered.
It was why there was some dismay at City that Aguero chose to play for Argentina against Paraguay, despite suffering a calf complaint only five days earlier and Guardiola is determined to ensure Aguero's conditioning drastically minimises the risk of future injuries.