David Luiz has admitted frustration at being rested for some key games amid Chelsea's recent fixture pile-up but has still backed the logic behind Rafael Benítez's policy of squad rotation as the reigning European champions prepare to chalk up a half-century of matches for the campaign in Thursday's Europa League tie in Romania.

The 50th game of a draining and too often traumatic season will see the Londoners confront Steaua Bucharest, conquerors of Ajax on penalties in the previous round, in the first leg of their last-16 tie at the National Arena. Benítez is expected to recall his captain, John Terry, and partner him with Gary Cahill in central defence, potentially pushing David Luiz into a midfield brief in the first of three cup games in eight days. Both Ramires and Victor Moses have been rested and remain in England, while Juan Mata, Frank Lampard and Ashley Cole are likely to start on the bench with one eye on Sunday's FA Cup quarter-final at Manchester United.

Benítez claimed convincing his players of the need to be rested is the "hardest part" of his job, which felt a considerable admission given the opposition he has faced from supporters since taking up the reins in November. "I don't feel good [about being left out]," said David Luiz. "It depends: sometimes, if I'm hurting in a part of my body and I feel I need to rest, then it's easy to understand. Other times, though, when you are on the bench but are fit, it's a really bad feeling. That's just the truth. I don't like it, but I understand that, sometimes, you need to pick other players and plan for the games ahead.

"You need to understand this is a team game. This is the quality of sport. If you want the team just to be about doing your thing and to play all the time, play tennis or a sport that is for individuals. This is a collective game. Sure, all the players in the world want to play and no one wants to sit on the bench, but that [frustration] only lasts a couple of minutes. Afterwards, in your head, you realise this is normal."

Benítez has long been hampered by a cluttered schedule, with his team still fighting on three fronts and the need to secure a top-four finish in the Premier League and, therefore, Champions League qualification clear and obvious. That much has been reiterated by the chief executive, Ron Gourlay, this week. "The point is to convince the players they cannot play every single game," said the manager. "Some want to play every match so I have to say: 'Listen, I know that you can do well but, just in case you will be tired, we need fresh legs. We have to use the squad.' That is my job, to manage the squad. It is the hardest part. When we have everyone training well it's really difficult to make a decision as to who plays and who doesn't."

While there will be changes ahead of the daunting trip to Old Trafford, Oscar, who has scored six times in European competitions this season – only Cristiano Ronaldo, Edinson Cavani and Burak Yilmaz boast more – should feature behind Fernando Torres, who replaces the cup-tied Demba Ba. Regardless, there is belief within the travelling Chelsea squad that they will have the quality to impose themselves upon the Romanian league leaders – Laurentiu Reghecampf's side are 12 points clear at the top of their division – before seeking to exploit any lingering disappointment in the United ranks following their own elimination from the Champions League on Tuesday.

"It's difficult when you've been knocked out of an amazing competition like the Champions League," added David Luiz. "Your confidence is not the same. The happiness inside your heart is not the same. Maybe that will give us an advantage [on Sunday]. That will be a massive game, but for now we concentrate on the Europa League. Chelsea are a big club and of course we want to be in the top four and play in the Champions League next year, but I also want to win the titles we're going for this year.

"I don't go into the Europa League and think: 'Oh, I don't care.' I've never won this competition, so I want to feel what it's like to win this title. It's a European title. I was born in Brazil, and in South America the dream for all players is to make it to Europe. Now I have an opportunity. Why not take this great opportunity to win another European title. Chelsea don't have this title. I want to win it just as much as I did the Champions League last year."

Steaua Bucharest (4-3-3; possible): Tatarusanu; Rapa, Gardos, Chiriches, Latovlevici; Pintilii, Chipciu, Tanase; Tatu, Popa, Rusescu.

Chelsea (4-2-3-1; possible): Cech; Azpilicueta, Cahill, Terry, Bertrand; Mikel, David Luiz; Oscar, Benayoun, Hazard; Torres.

Referee: S Karasev (Russia).