[Programming note: Manchester City vs Chelsea will be shown LIVE on Sunday morning starting at 10:45am EST on NBC Sports Network]

Manchester City’s lineup is dotted with top players at every position and each individual has an distinct value to the club.

Vincent Kompany is the captain and orchestrates the squad from the back. David Silva is the midfielder maestro who pulls the strings in the attack, while adding his own scoring touch from time to time. Sergio Aguero – when he’s 100% healthy – is probably the best striker in the Premier League and one of the top five strikers in the world.

But the key to Manchester City’s domestic and European title hopes lay squarely upon the shoulders of their big man in the midfield, Yaya Toure. Any success that City has had over the past three years, has emanated from the play of the marauding Ivory Coast international.

Since his arrival in England, Toure has dominated opponents with his size, pace and strength in a league where those qualities are particularly held in high regard.

Historians will always remember Sergio Aguero’s title-clinching, injury-time goal against Queens Park Rangers in 2012. But the moment that gave Aguero the chance for his championship heroics came a week earlier in Newcastle.

With the match level at nil-nil in later stages of the contest, Manchester City were on the verge of having control of their future ripped out of their hands by Alan Pardew’s Newcastle United side.

To that point, City were even with Manchester United at the top of the Premier League table. The only thing separating the two Manchester club’s was City’s superior goal differential.

But a draw against fifth-place Newcastle would have given control back to Manchester United, since Sir Alex Ferguson’s side had played earlier in the day and had already won.

Newcastle were resolute and had refused to allow City to breach their defence in the contest at St James’ Park.

That is until Yaya Toure took matters into his own hands by playing a ball to Sergio Aguero, moving himself into better position to receive the return pass, then cleverly curling a strike around Newcastle defenders and past goalkeeper Tim Krul to give City a huge lead and an even bigger moment of relief.

You could see the enormity of the goal in the way Toure’s teammates celebrated it following its arrival in the back of Newcastle’s net. City players swamped the 6-foot 3-inch midfielder, to the point where you could barely see the Ivorian underneath the pile of his City teammates.

He would then a second goal in the match to secure all three points and place his club’s title-winning hopes back in their hands.

Not to be forgotten is that Toure single-handedly ended Manchester City’s 35-year trophy drought a year earlier during in his debut season with the club.

After joining City from Barcelona, the Ivory Coast midfielder put in a Man of the Match performance against Manchester United in the FA Cup semi-final at Wembley; and scored the only goal of the contest as City beat United, 1-0.

He continued his Wembley success by scoring the only goal during the FA Cup final against Stoke City in May 2011.

It can be argued that had Toure not scored those Wembley goals, Manchester City may still be trying to win their first trophy since 1976.

But he did and Manchester City have now won two Premier League titles, a FA Cup and a League Cup since the former Barcelona midfielder’s arrival at the Etihad Stadium.

Toure’s form has dipped at the start of the recent league campaign and the player is facing criticism after a poor performance during City’s disappointing 1-0 loss at Bayern Munich earlier this week. Pundits are pointing to his physical appearance, body language and simple dip in form.

During the summer, there were rumors circulating around the club of Toure’s “unhappiness” with City officials. The player had voiced his complaints about the reigning Premier League champions and speculation began to grow about the 31-year-old’s future in Manchester.

Toure also suffered a huge personal tragedy when it was learned that his younger brother Ibrahim had died prior to the Ivory Coast’s World Cup defeat to Colombia in June. Yaya and his other brother Kolo were given the earth-shattering news immediately after the match ended.

It was later learned that City would not allow Toure time off to spend with his younger brother while he was his health was failing; due to his club’s post-season commitments in the United Arab Emirates.

All of these events – and the fact that Toure has not seen a significant time away from football during a World Cup year – have likely taken a mental and physical toll on the midfielder’s mind and body.

The other issue could be that Toure’s body is simply beginning to break down on him.

For the past nine seasons, the Ivorian has played on the highest levels in Greece, France, Spain and England; while also representing his home country on international duty. Toure is a physically imposing, athletic freak of nature – but he’s not Superman. One day his body is going to fail him.

Hopefully for City fans that isn’t the case and the player is simply suffering through a tough patch. Because as Toure has shown during his time in England, he is extremely instrumental in Manchester City achievements.

The midfielder’s return to form will be the key to the club’s domestic and European successes this season.