Premier League club Chelsea spent more than £70million over the summer to sign Havertz from Bayer Leverkusen.
The 21-year-old has endured a mixed start to his Blues career, scoring a hat-trick in an EFL Cup win over Championship outfit Barnsley but failing to make much of an impact in his four league appearances to date.
Havertz played 89 minutes of Germany’s 3-3 friendly draw against Turkey on Wednesday night and Nicol felt he drifted in and out of the game despite providing two assists.
‘It’s weird [with Kai Havertz],’ the former Liverpool and Scotland defender told ESPN.
‘Some of the things he did [against Turkey] were really delicate and simple and well executed.
‘But then he disappeared for long periods so he kind of played the way he does for Chelsea.
‘He’s kind of nowhere and then he will have a lovely touch or a nice pass with the perfect weight. He will do something that keeps you interested.
‘Officially he had two assists but he was in and out of the game and that’s not what you would expect from a guy who has cost so much money.’
Chelsea defender Antonio Rudiger, who was heavily linked with a move away from Stamford Bridge over the summer, also featured for Germany in Cologne on Wednesday.
Blues striker Timo Werner missed the clash, however, due to illness.
‘We are still waiting for the expected explosion of goals from the newer players,’ Nevin told the club’s official website.
‘Obviously Kai Havertz, Ben Chilwell and Timo Werner are each already off the mark, but it still feels like Timo and Kai are just bubbling under ready to explode onto the scene.
‘For once I think the Chelsea staff might be absolutely delighted to see many of these players leave on international duty, but why?
‘I reckon the likes of Kai and Timo both need as many games as possible to get themselves not only up to their own levels of mid-season match fitness, but higher still to the level expected week in and week out in the Premier League.
‘Unless they are injured on international duty, they will all come back in better condition than when they left, especially if they can get a full game or two under their belts for their own countries.’