However, perhaps the most comical and costly transfer misstep was the decision to sign Didier Ndong for a club-record fee of £13.6m.
He had just two seasons at the Stadium of Light, making 54 disappointing appearances and overseeing the relegation of the club from the Premier League. This marked the beginning of their slump, from which they are only now recovering.
To swap this out for a man said to have an attitude which makes him a “waste of space” – in the scathing words of Josh Bunting – is a huge downgrade. From having someone who fell in love with the club to splashing out on an apparent mercenary, it is decisions like these which explain Sunderland’s fall from grace in the late 2010s.
Ndong’s performance during that relegation season was disappointing given the outlay on him, with an average SofaScore rating of 6.73.
He also earned £32k-per-week whilst at the Stadium of Light, further exacerbating the amount spent on the flop. This remains the highest wage that he has been paid in his career and takes the money that the club spent on the midfielder up to an eye-watering £15.2m.
Ndong was at the club for 112 miserable weeks and is perhaps indicative of the downfall of Sunderland from 2016 to this year.
Now playing for Dijon in French Ligue 2, the Gabon international ended his bleak tenure at the Black Cats with the termination of his contract after going AWOL. It was a fitting end to a terrible stint on Wearside, and the start of their slump down the football pyramid.