Peter Kox and Maxime Martin will miss this weekend's FIA GT1 World Championship event at the Slovakiaring.
The pair, who drive for the Reiter Lamborghini and Valmon Aston Martin squad respectively, have prior commitments to race in ADAC GT Masters, which is holding its third round of the season at the Sachsenring in Germany. Reiter has signed Porsche Supercup podium finisher Stefan Rosina to replace Kox. The Slovakian, who will co-drive Darryl O'Young, last competed in the series in 2010.
The Valmon team has not named a replacement for Martin yet, but has confirmed that it is switching from old-spec Aston Martin DBRS9s to the new Vantage GT3 models for the coming weekend.