well it depends on the player, and how good/old they are. If you have a young kid who trains well he may experience a pop and a bit, but if you have an old player that doesnt train well he may just go down.
However with all stats its not just 5 or 6 it ranges from 5.0 to 5.9 then 6, so even if your player doesnt experience a pop, their decimal point will probably have increased.
if your player is only going to drop one level in their game shape i would expect training it to just cancel out.