Roster controversy has seeped into the 2018 World Cup and the event hasn't even started yet.

As the world's top 32 teams from qualifying head to Russia later this month, a number of managers already are under fire for the players left off their squads. Some teams, like France and Spain, have so many quality players that someone had to be left out.

However, fans like to complain even though managers likely have specific reasons for picking the players they did.

For argument's sake, here are some of the top players left off Word Cup rosters and why fans have legitimate gripes:

Alvaro Morata, Spain

The ex-Juventus and Real Madrid star got his Premier League debut off to a good start with Chelsea, scoring 10 goals before the new year. But 2018 proved fruitless for Morata, scoring just one league goal in five months, ultimately losing his starting job to Olivier Giroud.

Morata was an important member of Spain's qualifying campaign, but his recent poor form and poor attitude at Chelsea kept him off the World Cup roster. He is now being linked with a move out of England after just one season at Stamford Bridge.

Mauro Icardi, Argentina

Few players rose in stature as much as Icardi last season, scoring 29 goals in 34 games for Inter Milan. But the 25-year-old forward was the odd man out in Argentina's crowded attacking group featuring Lionel Messi, Sergio Aguero, Gonzalo Higuain and Paulo Dybala.

Icardi has experienced some off-the-field drama but has long been considered one of the elite European talents. With Aguero and Higuain largely failing to live up to expectations for Argentina, this could have been Icardi's time to shine on the national stage.

Alex Sando, Brazil

Entering the 2017-18 club season, Sandro was regarded among the best fullbacks in the world. He was being heavily linked with Manchester United and Chelsea, while displaying blistering form with Juventus.

But Sandro struggled last season, sometimes falling out of favor with his manager. The result was Brazil looking another way for fullback help this summer, while Sandro will again be a prominent member of the summer's rumor mill.

Karim Benzema, Alexandre Lacazette and Anthony Martial, France

Benzema had already fallen out with French manager Didier Deschamps, but fellow forward Lacazette and Martial are new to the snub party. While Lacazette (Arsenal) and Martial (Manchester United) endured frustrating seasons, both are talented enough to have helped Les Bleus in Russia.

In addition to the three forwards, stars such as Aymeric Laporte (Manchester City) and Adrien Rabiot (PSG) were also kept off the 23-man roster. France clearly decided to pick players with good attitudes, which may work out for them with a deep talent pool.

Leroy Sane, Germany

Possibly the most shocking omission from the World Cup is the fleet-footed Manchester City winger. Sane scored 10 goals with 15 assists in the Premier League this season, helping City win the league by a commanding margin.

Sane was dropped for Julian Brandt, a 22-year-old winger from Bayer Leverkusen, and Julian Draxler, the PSG star who has been favored by manager Joachim Low. Jaws may have dropped at the stunning omission, but Germany is still among the favorites to repeat as champion.