This is my personal experience:
If the fruit is on the ground, then it's probably too late. The Eucalyptus seeds are inside that cup. The cup per sei is not a seed. So, what you need to do is let the fruits ripe while they are still in the tree and keep an eye on them everyday. Once you see they are about to open, cut the stem bearing the fruits and put them in a big flask, jar or bowl. Place it in a dry place, away from sunlight. After a couple of days you'll be able to see the tiny seeds, that where released from the cups. Those are fine to sow.
If you take a look to the fruits that are on the ground, you'll probably see that they are open.
Hope this helps.