Ivanovic and Pereira both tested positive for coronavirus before the clash against Tottenham on November 8.
Robinson then posted a positive result whilst on international duty with the Republic of Ireland.
Ivanvoic and Pereira both resumed training with Albion during the international break while Robinson reported for duty yesterday after completing his 10-day isolation period.
But while those players are back, Bilic confirmed one or two other players have also tested positive and are now doubts for Saturday's trip to Old Trafford.
"Matheus and Branislav are back in training," the boss said.
"They have quarantined and tested negative so they are back.
"We have a few other players who were positive. so they haven’t trained for a few days and we are waiting for their results.
"I can't say their names. Hopefully, they will be back for training tomorrow (Friday), maybe today (Thursday).
"A few of the guys who were on international duty, they will be back today (Thursday) and have to do the test again as soon as they land.
"Hopefully, they are going to go be good.
"But we do have a few cases, yes.
"The good thing is that Pereira and Ivanovic and back. They have been training the whole week.
"So they will be fine for the game against Man United."
Asked about Robinson, Bilic continued: "Callum Robinson tested positive but he was tested again last night (Wednesday) and he is negative so he is good. He is good."
Bilic revealed a few of his staff have also contracted COVID-19.
But while the positive tests have not been ideal preparation for the Man United game, the boss is still pleased with the work that has been done during the international break.
"The club has been really great.," Bilic said when asked how tough the last fortnight has been. "We are where we want to be. We want to be present and influence the situation as much as we can.
"We are listening, we are in constant talks with the authorities – with the Premier League and with national teams.
"Yes, we have had a few cases and we had it with Branislav and Pereira and Callum.
"We have had a few cases with the staff also. They have been away for the last 10 days and now we are waiting for their results.
"We are doing everything we can.
"But I have had enough players to train and I have to praise them because the quality of training we have had during this international break has been great.
"It gives me a big expectation and big hope for our coming games, starting with Man United.
"We are still waiting for a few players who were on international duty who have to be tested but it looks good."