Havertz joined Chelsea last summer in a £71million transfer deal from Bayer Leverkusen, where he had thrived, scoring 46 goals in 150 matches.
But the Germany international initially struggled to make an impact at Stamford Bridge and was often benched by former manager Frank Lampard.
Havertz’s form has improved since Thomas Tuchel replaced Lampard in January and it was his goal that fired Chelsea to Champions League glory in the final against Manchester City last week.
Wenger is a big fan of Havertz and admits he was surprised by his early struggles in west London.
‘I believe that Havertz was very disappointing at the start,’ the former Arsenal boss told beIN SPORTS. ‘I liked him and I was quite amazed how much trouble he had at the start to settle.
‘He adjusted, adapted, he came back, he suffered, he spent his period on the bench and came back again. To me, he is a very promising player. I would bet on him for the future.’
Wenger has also rated fellow Champions League winner Werner, who endured a mixed first season at Stamford Bridge, scoring 12 goals in 52 appearances in all competitions.
‘I like the quality of his runs,’ Wenger added. ‘I like his movement, but he’s not… we see his conversion rate with the number of chances he has.
‘He’s not good enough to say, but he will be absolutely the favourite to be the player of the tournament [Euro 2020].’
Both Havertz and Werner will hope to help Germany win this summer’s Euros but Wenger does not rate Joachim Low’s side as contenders to win the tournament.
He said: ‘Honestly, I’m not very confident for Germany. They have lost the belief.
‘The Germans, to be successful you need in the team a combination of hunger, belief, aggression, and that you’re capable to fight the doubt. I believe in Germany belief has gone.
‘Another hurdle, is that it be the last tournament Joachim manages. To be completely honest, I have not seen a team do well when the players know that the manager will not there anymore after the tournament.’
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