Following a challenging 2022-23 campaign with a lack of game time at Bayern Munich, the 21-year-old opted to make a £34m transfer to Liverpool on the final day of the summer transfer window.
Gravenberch was then called up to the Netherlands Under-21 squad in September, but turned down the chance to represent his country and told the Dutch FA that he wished to focus on settling into life on Merseyside.
The midfielder's decision was criticised by senior coach Koeman, while Under-21s boss Michael Reiziger was also left unimpressed and claimed that the youngster "made the wrong choice".
Despite Gravenberch's withdrawal, Reiziger's side won two Euro Under-21 qualifiers without reply against Moldova and North Macedonia last month, beating the former 3-0 in Waalwijk and the latter 2-0 away from home.
Gravenberch has since started three of his seven appearances for Liverpool in all competitions, scoring once and providing one assists across two Europa League group-stage matches, as well as setting up a goal in a EFL Cup third-round win over Leicester City.
However, the midfielder has been omitted by the Netherlands from both their senior and Under-21 squads for this month's international break, with Koeman stating that he still has a "certain opinion" of the youngster.
Discussing Gravenberch's omission when speaking to reporters, as quoted by Dutch news outlet Via Nu.nl, Koeman said: "We do have a certain opinion about cancelling the Dutch Juniors.
"He hasn't played much yet (for Liverpool). I still think he's a great talent and I hope he will play a lot at Liverpool and continue his development. Then he will certainly be a player for the Dutch team."
In a separate interview with Reiziger, the Dutch Under-21s boss added: "It would be strange if it were now over with him [Gravenberch] at the Dutch Juniors. He is a boy with a lot of potential and he is still young.
"I think that a person always deserves an extra chance. Not everyone makes the best decisions or one where you see the consequences of this.
"Nigel [de Jong, director of football at the KNVB] has had contact with him, but I have not. It was not an option to call him up now. The signal has now been sent to him, but you are still busy with a group. It is something you have to want to belong to.
"I don't know if this is a one-off. But we are not going to write off young players anyway."
Gravenberch has made 11 international caps at senior level for the Netherlands since and including his debut in March 2021, while he has also represented the Under-21s 11 times since September 2020.
The Netherlands' decision not to call up Gravenberch this month comes at a time when they are having to cope without a number of injured players including Liverpool's Cody Gakpo, Memphis Depay, Frenkie de Jong, Matthijs de Ligt, Sven Botman, Steven Berghuis and Teun Koopmeiners.
Koeman's senior squad are preparing for Euro 2024 qualifiers against France on Friday and against Greece next Monday, with the Oranje currently sitting second in Group B and six points behind leaders France with a game in hand.