Medicals aren't about assessing injuries but finding out about long term medical problems. Ba's knee is clearly a cause for concern since he's failed medicals at Stuttgart and Stoke over the past two years.
What? Of course they assessing all injuries. The clubs doctors want to check it, and if i am not mistaken, something we have to do to insure the player...
My point is they're not just about just looking at immediate injury concerns. Gosling and Ireland may have been crocked when they arrived but their problems are relatively short term, whereas Ba is 'fit' but has a long standing complaint.