Howe says Bruno is devastated after learning that he faces at least six weeks on the sidelines with the hamstring injury suffered in the late stages of the midweek win at Tottenham. The Brazilian is not expected back until April, after the next international break.
Before then Newcastle have five Premier League games, including the Tyne-Wear derby against Sunderland and the two Champions League ties against Qarabag. If they advance, they'll also face their two last 16 Champions League games without their captain, who will also miss the FA Cup fifth round tie after the Magpies booked their place thanks to Saturday's 3-1 win over Aston Villa.
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Howe said: "The timeframe will be the timeframe. I don't think there's a miracle cure for him.
"I think it will be a couple of months. We're probably looking at the end of the international break in March for his return.
"Massive blow for us at a key stage of the season. He's devastated. But it is what it is, we can't do anything about it. We have to get him back safely and other players have to step up in his absence."
Newcastle were also without Yoane Wissa and Sven Botman at Villa Park.
Howe said: "We're not 100% sure on both. Sven is feeling his back from the game against Tottenham.
"We don't think it's a serious injury and he certainly won't be out for any period of time. But it was the right decision not to let him travel today.
"Yoane picked up a knock in training yesterday. Again, I don't think it's serious but he may miss a couple of games. Let's wait and see."