Liverpool right-back Trent Alexander-Arnold was surprisingly left out of the Reds' squad to face Porto in the Champions League on Tuesday.
Alexander-Arnold played the full 90 minutes in the recent 3-3 draw with Brentford and was then seen taking part in Liverpool training on Monday, so his inclusion in the squad for the group stage game seemed almost a certain.
However, as noted by the Liverpool Echo, the right-back has not travelled to Portugal and has instead remained at Anfield.
As of yet, no reason for his omission has been given. Liverpool have been 'tight-lipped' about the situation and did not even mention it in their pre-match fitness update, suggesting whatever has happened took them by surprise as well.
In his place, young Neco Williams has made the squad after overcoming an injury, but whether he is fit to make his first start of the season here remains to be seen. Jurgen Klopp also has centre-back Joe Gomez and utility man James Milner capable of filling in on the right.
What makes Alexander-Arnold's absence most concerning is the fact that Liverpool are due to welcome Manchester City to Anfield on Sunday, and if the Englishman has picked up an injury, his involvement in that game would be under threat.
City were dominant down Alexander-Arnold's side in their 1-0 win over Chelsea, with Jack Grealish and Joao Cancelo running riot, so Klopp will want his defence to be as strong as possible for the visit of the defending champions.
Virgil van Dijk is expected to be rested with that game in mind, while the Reds will also be without injured midfielders Thiago Alcantara and Harvey Elliott.
One player who has made it back to the squad is Naby Keita. The Guinea midfielder had been battling a foot issue but played a part in Monday's training session and was deemed fit enough for a spot on the plane.