Players will receive a one-match ban should they receive four yellow cards before the semi-finals of the Champions League.
This rule runs from the start of the league phase until the end of the quarter-finals. After then, all yellow cards are wiped out and players cannot be suspended for multiple yellow cards.
The same rules apply for both the Europa League and the Conference League.
During the opening three rounds of Champions League, 16 players received two yellow cards, meaning they are now two cautions away from a one-match ban.
Shakhtar Donetsk midfielder Marlon Gomes is on three yellow cards, putting him on the brink of a ban.
Players can also be suspended if they pick up six, eight or 10 yellow cards. This would also result in a one-match suspension every time a player hits an even number of yellow cards above four.
Red cards result in a one-match suspension, with Bayern Munich's Michael Olise missing his side's clash with Arsenal after being sent off against Viking in the previous round of fixtures.
Uefa may increase the length of a red card ban for serious offences such as violent conduct.
Which players have the most yellow cards in the Champions League?
Three yellow cards
- Marlon Gomes (Shakhtar Donetsk)
Two yellow cards:
- Akim Zedadka (Sabah)
- Alvaro Carreras (Real Madrid)
- Armando Obispo (PSV Eindhoven)
- Charles Vanhoutte (Feyenoord)
- Felix Lemarechal (Club Brugge)
- Giovanni Di Lorenzo (Napoli)
- Hakan Calhanoglu (Inter Milan)
- Ismail Jakobs (Galatasaray)
- Ismail Yuksek (Fenerbahce)
- Ivan Lepinjica (Sabah)
- Jan Virgili (Club Brugge)
- Josko Gvardiol (Manchester City)
- Kai Havertz (Arsenal)
- Santiago Mourino (Villarreal)
- Sergino Dest (PSV Eindhoven)
- Steve Solvet (Sabah)
This article is the latest from BBC Sport's Ask Me Anything team.
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