Bilic made four signings ahead of the new season but the Croatian has witnessed his side suffer back-to-back defeats at the start of the campaign.
However, Bilic - who is allegedly under pressure at the London Stadium - plans to make improvements before the closure of the transfer window.
The 48-year-old is quoted by Sky Sports News as saying: "We will see what happens in the last week of the transfer window, if somebody is going to leave or come in. Like most clubs we are ready to do something, both ways in case something good comes on our plate.
"I'm happy with the squad now. I would like to have one more and after that, if somebody leaves we have to fill that gap because we don't have a big squad.
"This is our squad for the season, or at least until January. We are happy but if somebody leaves we have to be ready to act."