From the notice of B2M, I am guessing that the injury must have been an old injury (from playing baseball?) and the dance routine must have aggravate it.
[INFO] B2M Notice - Young Saeng Injured and Solo Debut will be Postponed
Credit : http://www.young-saeng.com + (English Trans.) Ode's Blog
Hello this is B2M Entertainment.
We're here to deliver a piece of sad news to all fans who have been eagerly awaiting for Heo Young Saeng release of his first mini album and his solo activities.
While practising for his choreography, Young Saeng had hurt his hands, and until he recovers from that, all of his schedules and album have decided to be postponed.
All of you guys have been eagerly awaiting for him, and for the fact that we have decided for a delay is because Young Saeng health is of utmost priority more than anything.
After diagnosis, it was known that the fracture of the back of his hands and rusture of ligaments have been ongoing for already about 4~5weeks. For that, he is currently receiving treatment. Apart from Young Saeng hands, there aren't any other health issues that he's facing for now.
We'll do all our best that we can in ensuring the recovery of Young Saeng. As for his album activities and all, we will make another notice soon after he is discharged.Once again we wish to say sorry for having worried everybody.
We hope for Young Saeng fast recovery.
*all originally arranged broadcast schedules are now in midst of adjustments
All originally arranged broadcast schedules include: RECORDING, TV BROADCAST, etc.
He will make his comeback in May.