AC Milan midfielder Gennaro Gattuso is suspended this week with several others walking a disciplinary tightrope.
Gattuso will be much missed as AC Milan visit FC Internazionale Milano on Tuesday. The 27-year-old received his third yellow card of the tournament for a deliberate handball during the Rossoneri's 2-0 first-leg win against their city rivals. If a similar fate befalls Milan defender Alessandro Nesta or Inter midfield duo Juan Sebastián Verón and Cristiano Zanetti this time around, they would miss the first leg of any semi-final.
On Wednesday, Juventus FC's Alessio Tacchinardi serves the second game of his two-match ban for 'gross unsporting conduct' in the previous round against Real Madrid CF. Tacchinardi will need his team to overturn a 2-1 deficit against visitors Liverpool FC if he is to feature again in this season's competition.
Juve also have first-leg goalscorer Fabio Cannavaro, defender Lilian Thuram and midfielder Emerson one yellow card away from suspension while Liverpool defender Jamie Carragher, along with Stephen Warnock and Dietmar Hamann - who sat out the first leg through injury - face a similar threat.
Chelsea FC will again be without manager José Mourinho, who completes his two-match touchline ban as his side travel to FC Bayern München with a 4-2 advantage on Tuesday. Four of his players are one booking away from suspension including three defenders who started at Stamford Bridge - Ricardo Carvalho, William Gallas and Glen Johnson.
Midfielder Aleksei Smertin, an unused substitute last week, also runs the risk of a ban. Meanwhile, Bayern have similar concerns over defender Robert Kovac and midfielders Hasan Salihamidzic and Michael Ballack, all of whom are crucial to their chances of reaching the last four.
Finally, Olympique Lyonnais only have to worry about Brazilian defender Cris, after his two yellow cards in the group stage, when they play at PSV Eindhoven on Wednesday. The home side have the advantage after a 1-1 draw in France but four key men - Dutch internationals Phillip Cocu, André Ooijer and Mark van Bommel as well as Johann Vogel - are all a caution away from suspension.