Neither he nor centre-back John Souttar will be fit to face Motherwell on Saturday, although Michael Smith has a chance of playing.
Pereira, below, joined Hearts on loan from United last month but returned to his parent club after tearing a thigh muscle in only his second appearance. He has recovered in Manchester and is expected back at Riccarton on Monday.
“Pereira should be back up here next week and he should get a full week’s training,” confirmed Craig Levein, the Hearts manager.
Smith’s hamstring strain prevented him playing for Northern Ireland during the international break, whilst Souttar has been out for more than a month since injuring an ankle at Aberdeen.
“Michael Smith has been outside doing a little bit of running. That’s just the first step. It will be touch-and-go whether he makes Saturday or not,” added Levein.
“Souttar’s ankle is improving but it’s not allowing him to do certain things. The most difficult thing with the ankle is jumping and that is what is still causing him pain. We just have to wait until that heals. At this minute in time, it’s unlikely he will play at the weekend.”