As the Neue Luzerner Zeitung writes, Zug is careful not to leak any information about Josh Holden's injury, which was unspecifically called an "upper-body injury". It is only sure that nothing is broken.
As team manager Reto Kläy tells the same source, the injury does not seem to be too severe and they won't hire a replacement for Holden: "We re-evaluate the situation every day." However, Holden will probably also miss the games of the upcoming weekend.