Don't forget that he's already with the U23 if not the first team. A season bridged between both sides won't be a bad thing and will be a step up from last season, but at some point he would have to make a career choice.
I think there was some talk of that last year as well. Such rules are are quite common actually. When I still played football we had a similar rule that was there to prevent players from the first team playing in decisive games for the second team.