The pair played together at AZ Alkmaar before Reijnders left for AC Milan.
Bakker admits he can see Reijnders struggling with the pace of the Premier League, but insists the Holland midfielder will eventually adjust.
He told MilanNews.it: "They're both excellent leagues, but perhaps English football is different from Italian football. In the Premier League, he has less time with the ball and less space.
"However, I'm convinced he'll return to the levels he had at Milan, even though he might not score the 10 goals a season he had at AC Milan. But he'll definitely get back to scoring."
Bakker also stated: "After that excellent season (2022/23 at AZ), it was only natural that he would make the leap in quality. But when Milan called him, it was a bit of a surprise, even for me.
"His integration at Milan was very quick. Maybe I was a little surprised when he went to Milan, but I'm not now that he's at Manchester City."