Gundogan had earlier received lengthy treatment having been brought down by Joe Ralls in the incident that lead to De Bruyne converting the opener from an eighth-minute free-kick.
With City's chief creator standing over a free kick 25 yards (meters) out, Cardiff expected him to attempt to find the top corner. The fact remains though, we have seen some bad tackles go unpunished fully, and not just City players.
The Germany winger was scythed down by Joe Bennett, the Cardiff full-back who was booked at the time and later sent off for another ugly stoppage-time challenge on teenage substitute Brahim Diaz. Instead the Silva to excel was Bernardo, who thought he had scored a stunning goal and did set up Raheem Sterling's 19th of the season.
The Manchester City club captain hasn't played a single game since being taken off injured against Newcastle United in December previous year and has missed six games in all competitions since.
Pep Guardiola pleaded unconvincing ignorance over whether he will go back in for Arsenal forward Alexis Sanchez during the January transfer window as one of Manchester City's recent big-money recruit prepares for a reunion with his old employers. Both Manchester United and Liverpool have benefited from a midseason training break in Dubai this month, but while their rivals have been away in the sunshine, City have been playing (on average) a game every four days in recent weeks. Huddersfield are battling for survival in the Premier League, while Birmingham rank near the bottom of the Championship.More news: Trump to call for 'peace through strength' at State of the Union
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"Again, I have no words to describe my pride about my players and my team". But if City are still pushing for all major trophies in the spring, their winter workload could come back to haunt them.
Pep Guardiola's pursuit of all four titles has potentially hit a snag. But he will get his chance to impress in this FA Cup fixture. We hammer managers who play weakened sides in cup competitions for the very same reasons.
There are clearly teething problems with the system, which is why it is being trialled in England during selected cup ties.
Mason and Beck also got it wrong by disallowing Bernardo Silva's first half strike.
Now, though, Goal understands that City are interested in Eden Hazard. He has not given himself the best viewing angle to see it.
But a victory over the second-tier club in south Wales will guarantee City a fifth-round tie on the weekend of Feb 17, a week before the League Cup final.