Kai Havertz has all the qualities to be "world class" but was always likely to need time to settle in at Chelsea, according to Bayer Leverkusen's sporting director Simon Rolfes.

The Blues spent a reported £72million (€80m) to bring the Germany international from Leverkusen in September, yet he has so far struggled to justify the hefty price tag.

The attacking midfielder was one of several big-money signings during a busy close-reason recruitment drive, with compatriot Timo Werner - who arrived from RB Leipzig - also enduring a difficult start to life at Stamford Bridge.

Havertz has managed five goals and five assists, as well as 23 chances created (1.4 per 90 minutes) and five big chances created (0.3 per 90) in 25 appearances so far in 2020-21.

For comparison, during his final season at Leverkusen, he registered 18 goals (0.43 per 90), nine assists (0.21 per 90), 84 chances created (1.99 per 90), 20 big chances created (0.47 per 90) from 45 appearances.

Chelsea's struggles on the pitch this term saw club legend Frank Lampard sacked and replaced by Thomas Tuchel, and Rolfes feels it is unfair to focus purely on Havertz, who he is backing to show his true abilities in the Premier League.

"It's always difficult if you change country and a little bit of a different style. That's the same if we sign players," Rolfes told Stats Perform News.

"Some players need two days, some guys need half a year. For example, Moussa Diaby needs three-four months to adapt from France, although he was playing for PSG, to adapt to the Bundesliga.

"You have to have in mind when you sign players, that not everybody is directly from the first day there.

"I've followed Chelsea a little bit from a distance, but it's not only Kai or Timo Werner struggling a little bit, it's also the team – they expected more from the whole squad.

"That's not so easy if it's not working in the team and you come in as a new player. It's much easier if the team is working and you step in your best position.

"That's a process for Kai, to adapt to England and the Premier League. There is no doubt Kai is a fantastic player and has all the ability to play on the world-class level and although it's probably not his best six months, there is no doubt in my opinion."