Branislav Ivanovic has warned his Chelsea team-mates that "time is running out" if they are to salvage some pride, and potentially silverware, from a tumultuous season with the Serb urging the European champions to summon strength and unity for the run-in ahead.

Rafael Benítez's side travel to Old Trafford for their FA Cup quarter-final against Manchester United on Sunday having slipped 19 points behind the Premier League leaders and with their continued involvement in the Europa League threatened by Thursday's narrow first-leg defeat to Steaua Bucharest in Romania. That loss maintained recent inconsistent form and prompted a rallying cry from Ivanovic reminiscent of those usually delivered by the club captain, John Terry.

"It was disappointing for all of us in Bucharest, but we have to be honest with each other," said the defender. "We have to look in the mirror and see that a lot of things right now are not going how we would like them to. But we have to be strong, we have to stay everybody together and try to finish the season, if we can, at the highest level. We are not playing at the level we know we can. If we are realistic this has become normal, and we have to change this quick, because games are passing us by. One by one.

"Time is running out for us, and if we want to change things we have to show more character: to play as a team, show fighting spirit as a team. This team was in the same situation last season, and we finished that season well. We have to show the strength to change everything because, from now on in, every game for us is going to be harder and harder and much more difficult. It's not all about fighting spirit. We have to be honest with each other, with ourselves, and try to change this as quick as possible."

Chelsea have dominated the FA Cup over the last six years, claiming the trophy four times in that period, yet the prospect of recovering lost momentum at United feels daunting, particularly with the hosts having suffered their own disappointment in Europe in midweek. Benítez will make six or seven changes to his lineup in an attempt to inject energy back into his side, with Terry likely to drop down yet again on to the bench potentially alongside Frank Lampard. But the visitors will still arrive braced for a backlash.

"This is a game for us to show character, and a game to react to what happened in Bucharest," added Ivanovic. "We have to be mentally ready because we have two days less to prepare for a game which will be difficult and physical.

"The gap between us and them shows we have not done well enough this season. That is something for us to be thinking about. So this is going to be very tough – one of the biggest challenges for us this season. But it's not the time to look back at what's gone wrong. We have to look forward and try and change our situation from now on in, to believe we can do better between now and the end of the season."