Howe hopes to have the teenage midfielder back in the next fortnight, but says the Magpies have been advised to be "really careful" with the youngster.
Miley suffered a dead leg in the Champions League draw with PSG and the initial expectation was that he'd back in action after just a couple of days.
But the versatile 19-year-old then suffered with some "muscle disruption" which has resulted in a longer spell on the sidelines.
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Howe, who expects to have Jacob Ramsey back in the squad for Saturday's game against Everton after the midfielder missed Tuesday night's game against Qarabag with a minor hamstring injury, said: "We've just been advised with Lewis to be really careful with this injury.
"It was a dead leg, so a knock, which usually with a knock of that type it's maybe a couple of days and you're back, but there was a little bit of muscle disruption.
"He's had a couple of injections, I think he's got one more to come, so I think we're looking at a couple of weeks with Lewis.
"Because I think if we don't get the management of this injury right, it could rule him out for the season, so I think we're being careful to hopefully get him back in a good place."
The injury came at a bad time for Miley, who has enjoyed a fine season and established himself as a hugely important figure in Howe's squad. But the head coach says he's handling the challenge and frustrations well.
He said: "Typical Lewis. Not a massive amount of emotion, but that's a strength.
"He goes about his work in a really good way. I'm sure behind the scenes he's disappointed because he was in such a good place. He was playing really well whatever position we asked him to play and he was integral to what we were doing.
"And he also gave us a lot more choice and options to play different ways. So he's been a huge miss and we're desperate to get him back, but we have to respect the injury time scale given."
Howe says Tino Livramento continues to make good progress in his recovery from injury, with the full-back expected to be back in contention next week. Newcastle play Manchester United on Wednesday night.
Howe said: "Tino will be early March. We think he's still on track for that. He's done really well.
"He's been training now, not with us, but separately, running for a period of time.
"I think he's had a really good body of work behind him, so I think when he comes back, he'll be in a good place."
Newcastle will again be without Bruno Guimaraes against Everton, with the captain still in Brazil recovering from his hamstring injury.
Howe said: "I've had some good contact with Bruno. He seems very positive about his injury, how he feels. He's doing a lot of work as you say.
"I think he's been really well looked after as well, so credit to everyone that's doing that work with him.
"We hope that he can come back and really give us a push towards the back end of the season.
He's such an inspirational figure for us, that could be a huge boost for us.
"But we have to treat his injury carefully. I think it's a serious enough one for us to know that with any muscle problem, especially the hamstring, you've got to be really careful.
"I think the better he looks after himself now, the more we're going to be rewarded later in the season."