Guus Hiddink knows Chelsea will need to pass a big test against Paris-Saint Germain if they are progress in the Champions League this season.
The Premier League title-holders are in the French capital for the first leg of their round-of-16 tie with Laurent Blanc's side, but the two clubs have experienced starkly contrasting campaigns so far.
Chelsea started badly with only four wins from their opening 16 league matches, a run of form that saw Jose Mourinho sacked and replaced by Hiddink in December.
Things have improved somewhat under the Dutchman and Chelsea now occupy 12th in the table after going 10 games unbeaten.
Meanwhile, PSG are yet to lose in Ligue 1 after 26 games this season, have reached the final of the Coupe de la Ligue and are in the last eight of the Coupe de France.
"I agree it's 50-50 [for the tie]," Hiddink told his pre-match media conference. "Paris are building a very strong team, dominating the French league.
"To become a great club, a team must win the Champions League, and they're certainly aiming for it.
"On our side, we've been improving since December, but it'll be a great test to get to the next round."
He added: "We're growing. Everyone knows the current situation of Chelsea. We're improving step by step, with quality players.
"We are not yet where we want to be, to be able to impose our style of play, but we've had a string of games with dominant play from us."
"So we have to find the answer."
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