The Newcastle fans aren't angry with Mbabu himself, but instead are once again turning their rage towards the club hierarchy, questioning why the Toon let the 23-year-old leave the club without giving him a real chance in the first-team.
Mbabu signed for the Toon in 2013, but made just five appearances for the Magpies, all of which came in the 2015-16 season when Newcastle were relegated from the Premier League.
The Swiss defender was sent out on loan in the 2016-17 to Young Boys where he impressed, making 21 appearances. Despite his good performances, Newcastle took the decision to sell the right-back for a nominal fee of £675k.
Since then, Mbabu has become an integral part of a Young Boys team that has been going from strength to strength. They won the Swiss Super League last season, and have now qualified for the Champions League group stage for the first time in their history.
Newcastle fans have therefore questioned why a young, talented full-back was never given the chance to prove himself at St. James' Park, instead of being sold for a pittance of a fee.
Once again, Newcastle fans have a right to feel aggrieved. Since returning to the Premier League, the Toon have been particularly weak in the full-back positions. DeAndre Yedlin has impressed at times, however, if he gets injured or suspended then there is little cover.
Had Newcastle kept Mbabu, then they may have on their hands a pacey, attacking full-back, who at 23-years-old is still improving year on year.