The Eagles have scored a combined 10 goals from their previous three matches in the competition, most recently beating Estrela Amadora 4-0 in the last 16, while Belenenses left it late to seal a 3-2 victory after extra time against Fafe.
Benfica were unable to close the gap on rivals Sporting Lisbon at the top of the Primeira Liga on Monday as they could only draw 1-1 at home to Nacional, mounting more pressure on head coach Jorge Jesus.
The Eagles, who are desperate to return to the summit of Portuguese football after finishing as runners-up last season, are now three points behind Sporting having played a game more.
After three draws in their last four league matches, Jesus's men have dropped six points and fallen further behind their rivals, making the task of claiming their 38th league title a greater challenge.
Benfica now turn their attention to the Taca de Portugal with the expectation of a comfortable win on Thursday. However, recent cup performances in the last month suggest that their quarter-final match may not be so much of a walk in the park.
The Eagles have recently suffered defeats in the other two cup competitions, firstly losing the Supertaca Candido de Oliveira final against Porto before Christmas and then being knocked out at the semi-final stages of the Taca da Liga by Braga last Wednesday.
Jesus will be keen to ensure that they are not eliminated from a third competition in just 37 days and is likely to field the strongest side that he can to steer them into the semi-finals.
Belenenses ended a run of five league matches without a win as they secured a 2-0 home victory against Tondela on Monday.
First-half strikes from Mateo Cassierra and Tiago Esgaio helped earn Petit's side their third top-flight triumph of the season and saw them catapult out of the relegation zone and up seven places to 10th in the table.
Os Azuis do Restelo, who last won the Taca de Portugal in 1989, have been fortunate enough to face and beat three teams from lower divisions so far in the competition. However, they now take on one of Portugal's prestigious giants and will hope that they can cause an upset against a side currently out of form.
Belenenses have won only one of their last 20 meetings with Benfica – a 2-0 league victory in October 2018 – but a surprise win on Thursday would send them into their first semi-final since the 2012-13 campaign.
Benfica Taca de Portugal form: WWW
Benfica form (all competitions): DWWDLD
Belenenses Taca de Portugal form: WWW
Belenenses form (all competitions): LDLWLW
Benfica have recently been affected by an outbreak of coronavirus within the club, which has seen up to 10 first-team players forced to self-isolate.
Defenders Jan Vertonghen, Nicolas Otamendi, Alejandro Grimaldo, Nuno Tavares and Gilberto are all unavailable for selection as are Helton Leite, Odysseas Vlachodimos, Diogo Goncalves, Luca Waldschmidt and Everton.
Belenenses left-backs Nilton Varela and Chima Akas as well as central defender Eduardo Kau all remain sidelined with injuries, while attacking midfielder Richard and winger Silvestre Varela have recovered from COVID-19 and are available to play on Thursday.
Head coach Petit may decide to name the same starting lineup that beat Tondela on Monday evening.
Benfica possible starting lineup:
Svilar; Ferreira, Jardel, Todibo, Cervi; Weigl; Pizzi, Pires, Taarabt; Seferovic, Nunez
Belenenses possible starting lineup:
Kritsyuk; Phete, Silva, Ribeiro; Esgaio, Taira, Edgar, Lima; Cardoso, Cassiera, S. Varela
We say: Benfica 2-1 Belenenses
Belenenses will be hoping to build on Monday's league win and cause an upset on Thursday night. However, even though Benfica's squad may be depleted, they should have enough quality in the side they pick to progress to the semi-finals.