Actually, for the first leg I feel that if Roma feel unable to beat Milan at the San Siro then they just need to hold Milan to a draw and Roma just have to try to win in the second leg when they are the hosts. Arsenal is a difficult opponent who has even had a higher level of consistency than Roma this season. So even if Roma loses in this match, I feel that it is normal and De Rossi will not be blamed at all. Because Milan is indeed a strong enemy who is currently ranked 2nd in Serie A. It's just that if Roma manages to win then De Rossi's name will really get more attention. And his reputation will increase greatly.
First leg is going to be vital for the both sides with AC Milan also improved their performance in last few weeks which is good sign for them and with this improvement we can expect they could be big threat for the hot favourite teams in coming matches but for the next round game they are going to host AS Roma which is currently having impressive run have never won any game at the San Siro which is surely advantage for the AC Milan which needs to hold them with some good difference of goals because this could be give them good advantage for the second leg game which will be played at the Roma.
Until now, we have impressive strategy and performance from the De Rossi, and he surely deserved praise for this all with now in case of lost surely it's not all about his failure with he was at his best and bringing changes like these surely never been easy in quick time.