Since then, we’re unbeaten in 25 matches, winning 22 and drawing three.
Indeed, we’ve won our last 18 on the bounce, a sequence of results that mean we are now 10 points clear at the top of the Premier League table and in contention for all three major knock-out competitions.
It’s been a dazzling upturn in form, and Gundogan has hailed the manager’s impact in helping alter the course of our campaign.
“I’m not really surprised we've turned it around, but we knew we were not at our best,” Gundogan said.
“Our manager did the right things at the right time. He saw something was wrong and missing and he adjusted a few things - how we defend and how we play with the ball.
“That's why he is the best manager in the world. It’s incredible.
“I never thought in December about where we would be in February, but did I expect to be in this position? Maybe not.
“But I know we’re capable of a lot of things and knew we had great quality in the squad and knew we could go on a great run like we are.
“But it doesn't come automatically. You have to adjust, and we did. Everyone did a great job.”
We face Marco Rose's side in Budapest in the first leg of our Champions League last-16 tie.
They have slipped to eighth in the Bundesliga having picked up just two points from their last four matches, but came through a difficult Champions League Group B, finishing ahead of Shakhtar Donetsk and Inter Milan to finish as runners up behind Real Madrid.
Gundogan, an avid watcher of German football, says, at their best, Gladbach's attractive, attacking style is a match for any team.
"Gladbach have the necessary quality and can play active, aggressive football," he said.
"They have the right attitude and a good squad. Have a mix of players and are prepared to put in the work and in modern football you have to be able to.
"A mix of creativity, mentality and that leads to success.
"Qualifying for the Champions League comes from the work they have done in the last few years.
"Not everything works perfectly, that’s normal. On a good day, they can give anyone a game. They are a strong side.
"The difficulty was in the last couple of weeks. I've seen them a lot in the last few months and they have a great team, great spirit and on a good day can beat anyone, they did with Shakhtar Donetsk in the group stage.
"They have a lot of quality, energy and drive. They may have struggled for a couple of games but that does not deny that.
"We know how good they are and they want to play football. It should be a great two games."
We will have full coverage of Wednesday’s game against Gladbach right here on ManCity.com.
Our Matchday Centre will get under way at 6pm, with text updates throughout the evening meaning you won't miss a beat.
Our We're Not Really Here live matchday show starts at 7pm, when Kevin Horlock and Paul Dickov will be our guests.
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