5-4-1, 5-2mc-aml/r-1, 4-1-4-1. Depends on opponent, it's important to use (more defensive) counter formation. Put your tactics on defensive and hope for good result. I usually use mixed passing, own half press, zonal marking, hard tackling.
Defending is always though. You have to know exactly what are you doing and why, one mistake could cause defeat
Last season I've played against stronger team in CL. 1st match i used 4-1-4-1 against 4-4-2 and won 2-1 (home). 2nd match started 5-2mc-aml/r-1 against 3n-4-3, at HT 0-0. Since BP was around 50%, i pushed my cb-dmc from on dmc (4-5-1V). FT lost 4-0. Opponent manager hadn't watch both matches.