http://myespn.go.com/blogs/truehoop/...ling-Down.html
What caused Blair to slip to the seventh pick of the second round? Concerns about his knees. In high school, Blair tore both of his ACLs and had them surgically repaired. Blair's scar tissue essentially got re-absorbed by his body and the result left Blair with essentially no ACLs.
Although he's suffered no adverse effects ever since, Blair's is an unprecedented injury and one that scared off a slew of NBA executives. Though Blair literally has no ACL to tear, some team physicians feel that Blair could eventually develop a nagging issue that could wear him down a few years down the road. As a result, Blair ended up at the #37 pick of the draft, landing with San Antonio.