So if it goes well, he makes the U21 and then turns 22, whats next? What kind of player do you want after that, cause he's not even reached his prime.
The best financial move is likely to sell him now unless you plan to build a very well rounded player that has a ton of skills for a lower salary. The latter are very hard to find exactly how you want and extremely expensive. If you go that route then there's a good chance he wont make the U21 though, cause it will require lots of time training non primary skills.
"Well, no ones gonna top that." - http://tinyurl.com/noigttt