Olij drops out at the expense of rumoured Arsenal target Justin Bijlow. He missed a total of 25 games for club and country this season due to two different injuries and made a total of just 24 appearances for Feyenoord, but the 26-year-old striker has managed to convince Koeman of his fitness.
Young midfielder Timber, the twin brother of Arsenal's Jurrien, has been left out of the Oranje selection despite enjoying an excellent season with Feyenoord. He made 44 appearances and started 43 times, getting eight goals and 10 assists.
Ian Maatsen surprisingly turned out to be the third dropout and not Ryan Gravenberch. Maatsen was loaned out in January to Borussia Dortmund, with whom he will play the Champions League final next Saturday. He has made 22 appearances for Dortmund this season, getting three goals and two assists.
With the earlier loss of Marten de Roon through injury, Koeman only had to drop three more from the preliminary squad. De Roon is struggling with a muscle injury and was previously forced to miss out on the Europa League final.
In the run-up to the European Championship in Germany, which kicks off on Saturday 15 June, the Dutch will play Canada on 6 June and Iceland on 10 June. At the Euros, the Netherlands are in a group with Poland, France and Austria.
The full squad:
Goalkeepers: Bart Verbruggen (Brighton), Mark Flekken (Brentford), Justin Bijlow (Feyenoord)
Defenders: Virgil van Dijk (Liverpool), Nathan Ake (Manchester City), Daley Blind (Girona), Denzel Dumfries (Inter), Jeremie Frimpong (Bayer Leverkusen), Lutsharel Geertruida (Feyenoord), Stefan de Vrij (Inter), Micky van de Ven (Tottenham), Matthijs de Ligt (Bayern Munich)
Midfielders: Frenkie de Jong (Barcelona), Joey Veerman (PSV), Teun Koopmeiners (Atalanta), Jerdy Schouten (PSV), Georginio Wijnaldum (Al-Ettifaq), Tijjani Reijnders (AC Milan), Ryan Gravenberch (Liverpool)
Attackers: Memphis Depay (Atletico Madrid), Cody Gakpo (Liverpool), Wout Weghorst (Hoffenheim), Xavi Simons (RB Leipzig, on loan from PSG), Steven Bergwijn (Ajax), Brian Brobbey (Ajax), Donyell Malen (Borussia Dortmund)