The influential Coutinho sustained suspected ankle ligament damage during Liverpool's 2-0 win over Sunderland.
The influential Coutinho sustained suspected ankle ligament damage during Liverpool's 2-0 win over Sunderland on Saturday and could now be out until next year.
After replacing Coutinho, Origi scored Liverpool's opener and the Belgium striker believes there is sufficient quality in the squad to compensate for the unavailability of their Brazilian talisman.
"It's unfortunate with Philippe because everyone knows how good a person he is and I think he was in top form, so I hope it's not too bad," Origi told the Liverpool website.
"But I'm sure he will come back stronger and I always said that we have a strong group. Everybody has to help each other.
"I'm always ready. I believe I can help the team a lot this year and I believe I have the qualities to start in this team."
With Adam Lallana and Daniel Sturridge doubtful and Roberto Firmino unlikely to be risked after taking a kick to his calf against Sunderland, Origi seems certain to start against Leeds.
Sturridge scored twice as Liverpool, who lost to Manchester City in last season's final, overcame Tottenham Hotspur 2-1 in the fourth round.
Leeds, fifth in the second-tier Championship, overcame Norwich City on penalties and are the lowest-ranked team left in the competition.
There could be an upset on the cards in Tuesday's other fixture, where Premier League strugglers Hull City entertain Rafael Benitez's Newcastle United, who are flying high at the Championship summit.
Newcastle saw an eight-game winning streak ended by a 1-0 loss at home to Blackburn Rovers after Benitez made a raft of changes and he called on his team to raise their game for the trip to the KCOM Stadium.
"I think we have to take the positives. We were so good for so many games and that has to be the way to go forward," said the Spaniard.
"We have to analyse quickly what we did wrong and be ready for the next game in three days. That is a positive thing."
Manchester United will hope to shake themselves out of their domestic torpor on Wednesday when West Ham United return to Old Trafford just three days after the sides' 1-1 Premier League draw there.
United have drawn their last four home league games and have scored just four goals in their last five domestic fixtures on their own patch.
Speaking after the draw with West Ham, in which United manager Jose Mourinho was again sent to the stands, midfielder Ander Herrera expressed disbelief at the team's current woes.
"We're playing the right way and doing things the right way," said the newly capped Spain international, whose side beat holders City 1-0 in round four, in a Sky Sports interview.
"I think West Ham are a good side and they didn't get the ball for more than one minute (at a time), so it's unbelievable that we aren't winning these games.
"It's the first time in my career that I've felt something like this."
United will be without midfielders Paul Pogba and Marouane Fellaini through suspension.
Having started on the bench against West Ham on Sunday, Wayne Rooney will hope to return to the starting XI as he chases a record-equalling 249th United goal.
Arsenal will have more of a spring in their step ahead of their home game with Southampton, having ended a run of three successive draws by beating Bournemouth 3-1 on Sunday.
But Southampton were also bolstered by a positive weekend result, having consigned former manager Ronald Koeman to a 1-0 defeat on his return to St Mary's with Everton.
Fixtures (1945 GMT unless otherwise stated)
Hull v Newcastle, Liverpool v Leeds
Arsenal v Southampton, Man United v West Ham (2000 GMT)