Chelsea defender Branislav Ivanovic has admitted that the Blues will be going up against Manchester United in the FA Cup this weekend at the worst possible time.

The Blues suffered their fifth defeat in 2013 when they stumbled to a 1-0 loss against Steaua Bucuresti in the first leg of the Europa League round-of-16 tie last night.

While United host Chelsea at Old Trafford days after getting knocked out of the Champions League, Ivanovic believes that the Red Devils will be even more determined to win the quarter-final clash.

"It is going to be one of our biggest challenges of the season, especially playing them at this moment," Ivanovic told the London Evening Standard. "When you go out of the biggest competition in that way, it must be disappointing but they will be more motivated because of that."

Meanwhile, the Blues are currently placed in fourth in the Premier League table.