Are yellow cards wiped out ahead of semi-finals?

Yellow cards accumulated in UEFA club competitions from the beginning of the group stage were wiped out upon the completion of the quarter-finals.

All players left in the competition now have a clean slate. That means a single yellow card for a player in one leg of a semi-final cannot lead to them being suspended for the final should their team qualify. This ruling was introduced from the start of the 2014/15 campaign.

The official 2017/18 UEFA Champions League regulations state:

49.03 Single yellow cards and pending suspensions are always carried forward either to the next stage of the competition or to the UEFA Europa League in the current season.

49.04 Exceptionally, all yellow cards and pending yellow-card suspensions expire on completion of the play-offs. They are not carried forward to the group stage. In addition, all yellow cards expire on completion of the quarter-finals. They are not carried forward to the semi-finals.

49.05 Cautions and pending yellow-card suspensions from the competition or the UEFA Europa League expire at the end of the season.

The official UEFA Europa League regulations can be found here (see Article 48).