The 24-year-old picked up a hamstring injury during United's Champions League win over Basel last week, with initial estimates suggesting that he could remain on the sidelines for as many as 12 weeks.
Mourinho subsequently described those estimates as "complete nonsense" but was unable to provide a more precise timeframe at his weekly press conference this afternoon.
"I have no idea," he told reporters. "No idea. But, again, it's a great opportunity for other players to play and I trust them all.
"So I'm not going to cry or be counting the days until Pogba comes back, not at all. When he comes back, welcome, but until then, I trust my people."
Meanwhile, reports today have claimed that Mourinho has ordered Pogba to take a 10-day holiday to help speed up his recovery.