The Baggies boss is concerned by the size of his squad with less than three weeks to go until the Championship season starts.
This summer, Albion have sent six loanees back to their parent clubs, released five players, and sold two more for a combined £16m in Craig Dawson and Jay Rodriguez.
So far the Baggies have only signed Filip Krovinovic on loan from Benfica, and Bilic believes it's 'about time' his new club got moving in the market.
Speaking after a 3-0 defeat to Villarreal in a pre-season friendly, Bilic exclusively told the Express & Star: "As every West Brom fan knows, we need to get some players because we lost a lot of players last season and we need to replace them.
"At the moment, is it close? I hope it's close. It's not on me. I'm inside of course, but it's not me who is dealing and finishing the transfers. I hope (we make some), because it's about time.
"It's only three weeks (until the season starts). Like any other manager I would like to have had the players for the first day of pre-season but let's say it will be crucial for them to come next week."
Albion's greatest need is up front, where Hal Robson-Kanu is the only recognised senior striker following the exits of Rodriguez and Dwight Gayle, but Bilic also wants to add to his back-line after losing several bodies in defence.
Bilic continued: "We have some good strikers, but everybody knows we lost 50 goals from last season and that's very difficult to compensate from the squad within. It's as simple as that.
"I'm happy with some strikers we have, I'm happy with Hal, I'm hoping (Oliver) Burke is going to show his potential behind him, but look, we need more.
"It's difficult to replace Jay and Gayle. It's not the only area we're focusing on but it's the main one.
"You see the numbers from last season and this game. We are (currently) without (Ahmed) Hegazi, we are without (Craig) Dawson from last year, as well as (Tosin) Adarabioyo and (Mason) Holgate. That's four players (in defence). It's numbers."
Kyle Bartley was the only senior centre-back available against Villarreal, which meant 20-year-old academy product Dara O'Shea player the full 90 minutes.
The Irish defender was the only player on either side to stay on for the whole game, and he looked composed up until a late mistake allowed Villarreal in for their third goal.
Bilic said: "He's fit, he could be around it. He came to pre-season very focused, he's a good lad, had a very good season last year with Exeter.
"I know it's a different level but especially now we are without a few players, he's got a chance, and he's done really well so far."