#4 Russia vs Croatia
This is a proper bloodbath.
Russia has 5 players already on yellow cards, chief among them Golovin, Zobnin and Kutepov. Golovin, being the playmaker should be safe, but Golovin has a history of being short-tempered and not shying away from tackles.
Zobnin is more integral to the squad as the defending midfielder, while Kutepov has earned a name for himself at the heart of the Russian defense.
Both of them have a high chance of picking up a second yellow in the game because of Russia's predominantly defensive tactics, but there is no avoiding playing them.
Two other Russians -- Smolov and Gazinskii are also on yellows, but they are not part of the starting XI and do not carry much cause of concern.
Croatia has a whopping 8 players on a yellow - and four/five of them are part of its regular XI. Vrsaljko, the right back from Atletico Madrid picked up his yellow against Argentina and is generally a player who likes to get into 50/50 tackles.
Another cause of major concern is Ivan Rakitic, who also picked up his yellow against Argentina. Playing as the DM, he is heavily involved in the defense while Modric loiters forward, and is one of the best midfielders in the world - meaning that Croatia cannot afford to miss him.
Both of Croatia's forwards - Mario Mandzukic and Ante Rebic (who can also play in the midfield) are on yellow cards, while Brozovic who can play as a defending midfielder if Croatia opt for an attacking formation is also on a yellow card.
Corluka, Jedvaj and Pjaca - all of them who serve as substitutes, are also at the risk of suspension for the semis if they pick up a card against Russia.