Havertz - who finished the season by scoring the winning goal in the Champions League final - claims he was expected to hit the ground running in England upon arriving from Bayer Leverkusen.
"But it won't be that fast, everything is new and I really didn't play my best football at the beginning.
"I felt a completely different pressure than before in Leverkusen."
While Havertz says winning the Champions League has boosted his confidence, he admits it will count for little if Die Mannschaft fail to compete for international silverware this summer.
"We're with the national team, we have different processes and different goals here," said Havertz.
"Of course, this title gives me tailwind and a lot of self-confidence, but there's no point in feeling like a Champions League winner if you screw up the European Championship afterwards."