Rapid and Austria Vienna are long time city rivals, currently separated by only 2 points in the Austrian Bundesliga.
19 year old Austria Vienna star Valentin Grubeck was ambushed by 15 Rapid fans on Thursday night after leaving training.
The youngster suffered severe bruising to both his back and his chest. Grubeck is also going for a scan on his knee.
On Sunday the two rivals are due to meet in the Bundesliga.
Rapid released a statement on Friday, “Despite (still) lack of detailed information on the events of the SK Rapid want to repeatedly make it clear in this way that violence, whether against fans, even players or officials to condemn in the strongest terms and is not acceptable,”