Havertz has struggled since a £70million move to Stamford Bridge and has only featured as a substitute in each of Chelsea’s last four games.
There were high hopes for the 21-year-old this season after such a big-money transfer but Bosz has been confused by Lampard’s use of him thus far.
And while he praised the Chelsea manager for how he has handled any criticism of Havertz, he questioned what the ‘exact plan’ is for the German.
‘It’s really good that he protects him in the press, though. But in the end, you must deliver, you must score goals and make goals.
‘For a €100 million transfer you must play, and he isn’t.’
Bosz has previously worked with Havertz’s Chelsea team-mate Hakim Ziyech during his spell at Ajax manager and is not surprised he has settled quicker.
If there’s a free kick, he will just walk up and take it. He’s like that.’