Roma manager Eusebio di Francesco says his side face "a machine" in Barcelona but retains hope they can pull off an unlikely Champions League comeback.

The Italian side host the Spanish league leaders on Tuesday (19:45 BST) having lost the first leg of their quarter-final 4-1 at the Nou Camp.

But Di Francesco said: "Why not believe until the end and hope we can achieve something unprecedented?

"It's a really tough ask, but we have the duty to try."

Roma were beaten 2-0 by seventh-placed Fiorentina on Saturday and are now 21 points behind Serie A leaders Juventus in third place.

In contrast, Barca equalled the La Liga record of 38 games unbeaten as they overcame Leganes 3-1, with forward Lionel Messi scoring a hat-trick. They are 11 points clear at the top of the table.

"We're up against a machine," Di Francesco added.

"We must play with passion, heart and belief right up until the final whistle if we want to do the unthinkable."

'We have to play like it is 0-0'

Barca manager Ernesto Valverde remains cautious despite their first-leg lead

Despite Barcelona's domestic form and their three-goal advantage going into Tuesday's Champions League fixture, manager Ernesto Valverde insists his side are not already thinking of a place in the semi-finals.

"We can't take it for granted. We have to play like it is 0-0 because anything can happen," said Valverde.

"They are going to go for it. We saw in the first leg they have good players and we have to be prepared for them."

Barca left-back Lucas Digne remains out with a hamstring injury, while midfielder Sergio Busquets could be in line to return from a broken foot having been named in the 21-man squad.

Forward Philippe Coutinho is ineligible having played in the competition for Liverpool.

Roma will welcome back midfielder Radja Nainggolan and forward Cengiz Under, who were both injured for the first leg, but winger Diego Perotti is still sidelined with a calf problem.

'Roma believe they can frighten Barcelona' - analysis

European football writer James Horncastle

There is a chance of a comeback. It is a slim one. Roma believe because they thought they played well at the Nou Camp.

They scored own goals and were unlucky not to get a couple of penalties.

When most people would say the tie is gone, it was an odd decision to rotate and rest so many players at the weekend against Fiorentina.

It seems they believe in this exploit. They think they can do something - or at the very least frighten Barcelona.

Listen to the full preview of this week's Champions League fixtures on the Euro Leagues Football Show

The stats

• Only two teams in Champions League history have overturned a first-leg deficit of three goals or more - Deportivo La Coruna v AC Milan in 2003-04 and Barcelona v Paris St-Germain last season.
• Barca have not won any of their past six Champions League away games against Italian sides (drawn two, lost two).
• Roma have kept a clean sheet in five of their past six Champions League home games, winning the past three.
• Barca have conceded just three goals in this season's Champions League, fewer than any other side.
• Barcelona forward Messi has scored just two goals in his nine Champions League away games against Italian sides, with both of these coming against Milan (November 2011 and October 2013).

NB: There will be live commentary of the game on Joy 99.7FM. 

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