Celtic supporters have barely had time to enjoy their emphatic victory over Dundee United before another major talking point has emerged around the club.
The Hoops produced an impressive 4-0 victory at Tannadice to progress in the Premier Sports Cup, with Martin O’Neill’s side showing the kind of ruthlessness that will be required when the Champions League campaign reaches its crucial stage.
Yet the night was not without controversy.
Celtic’s opening goal sparked a major debate after the ball clearly struck Kasper Høgh’s hand in the build-up. Referee Steve McLean awarded the goal, VAR checked the incident and decided there was no reason to overturn the on-field decision.
Scottish FA Head of Referees Willie Collum subsequently explained that the handball was accidental and was not punishable because Høgh was not the player who eventually scored.
That explanation has done little to stop the noise from Rangers supporters and others who believe Celtic benefited from another controversial decision.
But while that argument continues to dominate social media, Celtic have been hit with something far more significant on the footballing side.
And it concerns one of the most important players in their squad.
Arne Engels has left Celtic for West Ham

Arne Engels has completed his move away from Celtic, joining West Ham United in a record-breaking £22 million deal.
The 22-year-old Belgium international has signed a five-year contract with the Hammers, becoming the most expensive player ever signed by an EFL Championship club.
On the surface, Celtic have secured an excellent financial return.
But losing Engels at this particular stage of the season could prove considerably more painful than the transfer fee initially suggests.
The midfielder was not simply another squad player.
He had developed into an important part of Celtic’s midfield and had accumulated 100 appearances for the club, contributing 17 goals and 22 assists.
He also leaves Glasgow with back-to-back Scottish Premiership titles, as well as Scottish Cup and Scottish League Cup winners’ medals.
More importantly, Celtic are now preparing for Champions League football.
Engels could have been playing on Europe’s biggest stage with Celtic this season.
Instead, he has chosen a completely different challenge.
From Champions League football to the Championship
That is perhaps the most surprising element of the transfer for Celtic supporters.
While Engels could have remained at Parkhead and competed for another league title while testing himself against Europe’s elite, he has opted to move to a West Ham side attempting to climb out of the Championship.
West Ham have made their intentions clear by paying £22m for him, but the fact remains that Engels is moving from a club with Champions League ambitions to England’s second tier.
For the player, the attraction is presumably the opportunity to test himself in English football and become part of a major rebuilding project.
For Celtic, however, it leaves a sizeable hole.
Martin O’Neill has already acknowledged that the club need to find a replacement, with the manager looking for a box-to-box midfielder who can provide genuine physicality.
That recruitment now becomes extremely important.
Rangers could be watching closely
And this is where the situation becomes particularly interesting for Celtic.
Rangers will undoubtedly be looking at the development of Celtic’s squad with their own ambitions in mind.
The gap between the two Glasgow clubs can change quickly, particularly when one side loses an important midfielder without immediately replacing him with someone of comparable quality.
Engels brought energy, technical ability and the willingness to contribute in both directions.
Replacing his numbers is one challenge.
Replacing his overall influence on games could prove an even bigger one.
If Celtic fail to bring in the right player, Rangers could potentially view the midfield situation as an area to exploit when the sides eventually meet.
Of course, losing one player does not suddenly make Celtic vulnerable.
The Hoops remain capable of putting together a strong squad and have already been active in the transfer market.
But the timing of Engels’ departure makes the next few weeks crucial.
Celtic have already started looking for a replacement
O’Neill has made it clear that Celtic are not simply going to accept the loss and move forward without reinforcement.
The manager wants a midfielder capable of adding physicality and energy to his team.
That is particularly important given the demands that will come with competing domestically while also navigating European football.
Celtic cannot afford to replace Engels with a player who merely fills a squad number.
They need someone capable of stepping into the midfield and maintaining the level of performance expected from a team chasing trophies.
That makes this one of the biggest pieces of transfer business still facing the club.
Engels leaves with an emotional message
The Belgian midfielder’s departure was accompanied by a heartfelt farewell to Celtic supporters.
“After two incredible years, it’s time for me to say goodbye to Celtic,” Engels wrote.
“I’m leaving with nothing but gratitude for the time I’ve had at this club.”
He added:
“I’ve experienced so many special moments, lifted trophies, created unforgettable memories and had the honour of representing Celtic. Wearing this shirt and playing in front of the supporters has been a privilege I’ll always be grateful for.”
Those words underline how significant his Celtic spell was.
But now the reality is that the Hoops have to move on.
The Tannadice controversy may continue to dominate the headlines for a few more days, particularly with Rangers supporters demanding answers over the VAR decision.
Yet the bigger concern for O’Neill is happening away from the referee’s office.
Celtic have lost a key midfielder just as their season is beginning to gather serious momentum — and if they fail to replace Arne Engels properly, Rangers could be waiting to take full advantage.