Silva was speaking in his match programme notes ahead of their preseason friendly defeat to Eintracht Frankfurt.
Only back-up goalkeeper Benjamin Lecomte has so far arrived.
“We hope we can strengthen the squad in the three or four positions we need to before the first game,” said Silva.
“Some positions are really short and we have to add players, yes or yes until the end of the market because it’s not what we expect in this moment of the season to don’t have at least one, two or three players we needed for the beginning of the season.
“We expected much more activity from ourselves in terms of recruitment, players in. Unfortunately, they are not here. The worst thing we can have now is more injuries. Jedi (Antonee Robinson) had the small surgery, it will take a little bit more time for him to be ready.”