Goal.com lists all the players who will potentially miss the first leg of the semi-finals should they pick up a booking in the return clash of the last eight.The stakes have been raised as we reach the business end of the 2011-12 Champions League. With only three rounds of matches to go before the two finalists are determined for the Allianz Arena showpiece, suspensions and bookings become an increasingly significant issue.The disciplinary system works as follows: When a player has picked up three cautions in three different matches, they are forced to serve a one-match ban. Unlike in previous seasons where yellow cards are wiped clean at certain stages of the competition, this term any bookings received in the group phase are carried over to and throughout the knockout rounds. But crucially, any cautions accrued in the qualifying/play-off stage that did not result in a ban are expunged.Once a player has served a suspension for picking up three single yellow cards, any subsequent odd-numbered bookings (fifth, seventh, ninth, etc.) will result in a further one-match ban.A red card, of course, means an automatic one-match suspension, and depending on the severity of the offence, Uefa could extend the ban.At the end of the season, all the disciplinary charts are wiped clean, though any outstanding suspensions will carry over into future campaigns.Here are the players who are only one booking away from missing the semi-final first leg should their sides progress:Alessandro Nesta Defender Massimo Ambrosini Midfielder Antonio Nocerino Midfielder Paulo Jorge Defender Marcelo Oliveir Defender Nektarios Alexandro Midfielder Marcinho     Midfielder Esteban Solari Attacker Ivan Trickovski Attacker Stephane Mbia Defender Jeremy Morel Defender Morgan Amalfitano Attacker Andre Ayew Attacker Jerome Boateng Defender Luiz Gustavo Midfielder Toni Kroos Midfielder Thomas Muller Attacker Artur Goalkeeper Ezequiel Garay Defender Luisao Defender Bruno Cesar Midfielder Javi Garcia Midfielder