Some players having their advancing age to blame for missing out on Europe's premier club competition, some simply bad luck and some a loss of form or the failing of their club as a whole. Whilst there are plenty of examples, we take a look at a few of the biggest names.
N'Golo Kante (Chelsea)
A World Cup winner with France and key player for Chelsea, Kante was named the Premier League's best player in 2016/17. However, his side's poor campaign last time out has deprived him of European football this season.
Andres Iniesta (Vissel Kobe)
A man who needs no introduction. This season will be the first since Iniesta's arrival on the football stage in which he has not competed in Europe's premier club competition, with his move to Japan marking the end of an era for a modern great.
Eden Hazard (Chelsea)
A World Cup semi-finals with Belgium, Hazard's only opportunity to shine in Europe this season will come in the Europa League.
Gonzalo Higuain (AC Milan)
His summer departure from Juventus means that the Argentine will also take a step down in terms of European competition, competing only in the Europa League.
Gabi (Al-Sadd)
Atletico Madrid's captain in their last to Champions League finals, Gabi called time on his career in Europe earlier this summer to join Xavi in Qatar.
Yerry Mina (Everton)
A man mountain for his country at the World Cup, Barcelona opted to cash in on the Colombian this summer a mere six months after buying him. Everton endured a frustrating campaign last season, struggling for much of the season despite a significant summer spend and failing to qualify for European competition.
Jordan Pickford (Everton)
One of the standout goalkeepers at the World Cup, Pickford enjoyed a solid debut season with the 'Toffees' last term, but it wasn't enough to push them into European contention.
Fernando Torres (Sagan Tosu)
A Champions League winner in 2012 with Chelsea, Torres followed international team-mate Andres Iniesta's lead by making the move to Japanese football this summer.
Benjamin Pavard (Stuttgart)
A virtual unknown before the World Cup, the defender is know one of the most sought-after players in world football. Rumours of a move to Bayern Munich continue to spread, but it seems we will have to wait to see the versatile stopper play in the Champions League.