Found this online and now I'm more at ease with the situation, seems like a good decision:
it is likely a very logical move on the part of the 49ers. Lattimore has been taking part in practice sessions, but on the off chance that something doesn't shake out with his training camp physical, it makes sense to retain the NFI option.
If Lattimore practiced on day one, and then the knee became a problem during that practice or otherwise in the early part of training camp, they would forfeit their use of the NFI list. If I had to guess, I could see Lattimore coming off the NFI list shortly after camp gets going. We can look to Kyle Williams and Kendall Hunter for comparisons. The 49ers placed both men on the PUP list to start training camp on July 20, 2013. They then activated Williams on July 25, and Hunter on August 10.