AC Milan head to Tottenham Hotspur with a slender lead to protect and their season once again in the balance following a damaging defeat at the weekend.
Stefano Pioli's side are a goal in front before Wednesday's last 16, second leg clash in London, Brahim Diaz's goal separating the two sides in the scrappy first encounter at the San Siro.
The seven-time European champions were completely outplayed in their 2-1 loss at Fiorentina, a mid-table team who before Saturday had not beaten anyone in the top half of Serie A this season.
That defeat, and Roma's win over Juventus on Sunday, left Milan outside Italy's top four on goal difference and with a rediscovered defensive solidity suddenly punctured.
Pioli insisted that his players weren't distracted by the importance of Wednesday's match but they were a shadow of the team which comfortably beat Atalanta last weekend.
Milan had gone into Saturday's match on a run of four wins – including the first leg against Spurs – in which they hadn't conceded a single goal.
But the remodelled three-man defence implemented by Pioli in the wake of a disastrous January which killed their league title defence fell apart in Florence, with Fikayo Tomori in particular having a dreadful night.
Pioli said on Saturday that he "more or less has an idea on who to play" and will have star attacker Rafael Leao back after he was suspended for Saturday's match.
Portugal winger Leao hasn't been the same player as before the World Cup but his presence will inject more threat into what was a toothless attack at the Stadio Artemio Franchi.
Milan have scored more than one goal just twice in their last nine matches, one of those a 5-2 home humiliation at the hands of lowly Sassuolo, and Leao is crucial to a new system which has closed gaps but has also dulled creativity.
In his absence Ante Rebic and summer signing Charles De Ketelaere did very little, Belgian attacker De Ketelaere a genuine conundrum for Pioli after an awful debut season in Italy which has produced more yellow cards than goals or assists.
De Ketelaere has the backing of Leao, whose powers of prediction were shown to be weak when he wrote on Instagram on Saturday "Cdk will score today, u saw here first".
The 21-year-old will almost certainly be back on the bench in London as Milan try to make this year's Champions League run their best since 2012, when they were comfortably beaten in the last eight by then-European champions Barcelona.
They will have to retain the solidity which gave them a first leg advantage if they are to stay in a tournament which they have won more times than any other club apart from Real Madrid.