However, City's latest quest for the trophy they most desire restarts this week with the first leg of their Champions League last 16 tie against Borussia Moenchengladbach.
As Pep Guardiola's first signing after arriving in Manchester, Gundogan joined a project determined to make a mark on Europe's premier club competition.
Despite six major trophies in the past five years and the likelihood of more to come this season with City also going strong in both domestic cup competitions, the Champions League has been a constant source of frustration for Guardiola.
Under the Catalan, City have not progressed beyond the quarter-finals in four attempts.
On the back of an 18-game winning run in all competitions, not for the first time the Premier League leaders find themselves tagged as Champions League favourites.
If this is to be the year that the Sheikh Mansour's billions of dollars worth of investment pays off in Champions League glory, Gundogan is likely to be a central figure.
The German is already having his best ever goalscoring season with 13 in all competitions, 11 of which have come in his last 13 Premier League games.
Gundogan's game is about much more than goals. A metronomic midfielder who rarely gives the ball away, he fits the profile as the type of player Guardiola loves.
“He is such an intelligent player," said the former Barcelona and Bayern Munich boss. "That's one of the qualities I appreciate the most, intelligence -- the players who understand everything that happens during the game and solve it as quick as possible."
'One of the best'
However, Gundogan's versatility also made him a favourite of Jurgen Klopp and Thomas Tuchel during his time at Borussia Dortmund.
"Ilkay was one of the best players I ever coached," said Liverpool boss Klopp before Gundogan scored twice against the English champions in a 4-1 win earlier this month.
"When you are smart and experience comes into play as well, then it's another jump in your performance level. I'm not surprised at all."
Gundogan's early time in England was disrupted by a cruciate ligament damage that ruled him out for nine months.
On his return he was faced with finding his way into a midfield three of Fernandinho, David Silva and Kevin De Bruyne that shone as City set an English top-flight record of 100 points to cruise to the title in 2018/19.
Now 30 and with Silva departed and Fernandinho playing a bit-part role at 35, Gundogan is one of City's leaders.
When De Bruyne was recently ruled out for a month by a hamstring injury, he scored six times in five games as Guardiola's men did not drop a point.
That maturity has also shown off the pitch as he has launched a charity campaign to help local bars, cafes and restaurants struggling to survive during the coronavirus lockdown.
Yet, like many of his teammates, Gundogan is yet to showcase his best on the Champions League stage in a City shirt after making his name in a run to the final for Klopp's Dortmund in 2012/13.
With his former boss now battling an injury crisis that has ravaged Liverpool's Premier League title defence, Barcelona on their way out, holders Bayern Munich showing signs of fatigue and Real Madrid no longer the force they once were, City may never get a better chance to finally make their Champions League breakthrough.
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