It was significant both in the stature of the player and the fee involved -- with Alderweireld having been one of the Premier League's most-consistent defenders over the past six seasons and rumoured to have cost £13 million.
Importing stellar names -- sometimes at exorbitant costs -- is nothing new for some of the Qatar Stars League's mega-rich clubs.
But with the Chinese Super League, for so long the biggest Asian players in the transfer market, now operating under its tightest-ever financial restrictions, could this pave the way for Qatari football to emerge as the premier destination in the continent?
Not too long ago, the CSL boasted illustrious names such as Carlos Tevez, Didier Drogba, Robinho and Nicolas Anelka to name but a few.
In a bid to increase sustainability, a raft of changes were introduced ahead of 2021 with total and individual salary caps for both domestic and foreign players.
The measures have immediately seen a drastic reduction of star power in the CSL with eight-time champions Guangzhou now remarkably boasting no import players apart from their handful of foreign-born but now-naturalised Chinese nationals.
Shanghai Port are perhaps the last bastion from the free-spending era of Chinese football, as they still have former Premier League trio Oscar, Marko Arnautovic and Aaron Mooy in their ranks although the latter two have been rumoured to be on their way out.
With Chinese spending waning, it has paved the way for Qatar to step up -- although it is not as though they have not already been luring some significant footballers to their shores previously.
Current champions Al Sadd have arguably made the biggest waves in the past decade with the signings of Spanish icons Raul and Xavi -- with the latter now managing the team after hanging up his boots two years ago.
While both arrived on free transfers, Qatari clubs have not shied away from spending.
The current transfer record belongs to Al Duhail from their purchase of Japan international Shoya Nakajima from Portimonense for a reported €35m in the summer of 2019. Curiously, they sold him at a significant loss to Portuguese giants Porto for just €12m three months later.
Just days before Al Duhail signed Alderweireld, Al Sadd announced the acquisition of Ghana captain Andre Ayew. While perhaps not in that top echelon of global superstars, the 31-year-old is still a proven goal-getter with Premier League and Ligue 1 experience, who probably could have continued his career in Europe had he wished to.
Yet Qatar are not the only ones capable of pulling off such high-profile moves.
Saudi Arabian teams have also been active ahead of the restart of their own domestic season with Al Ahli landing ex-Tottenham and Barcelona midfielder Paulinho, after he parted ways with Guangzhou via mutual termination of contract.
Meanwhile, Al Nassr - who, like Al Ahli, are still in the running to win this year's AFC Champions League - have bolstered their defence with former Everton man Ramiro Funes Mori, who was a part of the Villarreal side that beat Manchester United in the final to win the Europa League just last season.
And although they do not splash out in transfer fees, Japan has also proven to be an attractive destination with Andres Iniesta still playing for Vissel Kobe, while fellow 2010 FIFA World Cup winners Fernando Torres and David Villa also plied their trade there in recent years.
It is shaping up to be an interesting time for Asian football. Rather than having the biggest names all playing in the Chinese Super League, it could be a case where they are interspersed across the continent -- which would only add to the intrigue especially in a competition like the ACL, when the top teams from different countries face off against one another.
For now, however, Qatari football does look like it is making the biggest statements.