The 19-year-old midfielder was persuaded to stay at The Hawthorns by Bilic over summer, and signed a new three-year contract after six days after his old one ran out.
But he has struggled for time on the pitch so far this season, and has played just six minutes of Championship football under the Croatian.
Although the Baggies cannot buy any more players, they can loan players out to League One and League Two clubs as well as overseas outfits. But Bilic says Harper is going nowhere.
“Definitely not, we can’t,” said Bilic. “He’s a great talent. I insisted that he stayed, because he was out of contract.
“I rate him extremely highly and I have had meetings with him and talks. He’s improving a lot since then, the quality was never in doubt, and he’s getting there.
“At the same time we have a big squad and the guys are doing well at the moment.
“Like any other player he has to be patient, work hard, and wait for his chance that is going to come 100 per cent, probably soon.”
Oliver Burke has also fallen out of favour after featuring in the first three games of the season.
The £15million signing hasn’t played a single minute in the last three games, and hasn’t even featured in the squad.
There is a possibility he could be loaned abroad, but Bilic is planning for him to stay for now.
“With Burkey, what I like is he didn’t sink after not being in the 18,” said Bilic. “They reacted really positively, he’s also good.
“We have a number of strikers, we don’t have a massive squad, but if the players are not happy – not in a negative way – but I can understand it, we can talk about it.
“From my point of view, the both of them are staying, both of them are good players we are going to need this season.”