Two goals from Fabian Schar and an own goal from Alex Moreno put the Magpies 3-0 ahead at Villa Park before a late Ollie Watkins consolation.
It was a fantastic result for Howe and his side, but there was concern over Isak as he was substituted shortly before the half-time break, signalling to the bench that he needed to go off.
Miguel Almiron replaced the Swede and it did not cost Newcastle, but Howe is still waiting to hear the severity of the injury.
The Magpies boss identified it as a ‘slight groin issue’ and while he could not be certain, did not think it was a big problem.
‘We don’t really know. It doesn’t look too serious, looks like a slight groin issue. Fingers crossed we get him back quickly,’ said Howe.
On Isak coming off just before half-time, Howe said: ‘It was a total surprise to me. I didn’t see any incident, he just signalled to me that he had to come off. I was very unsure what had happened, it was out of the blue.
‘I’d like to say it was my decision but it was Alex’s decision [to come off]. He felt he had to come off.
‘We’re hopeful it’s not a serious injury, it doesn’t look too bad but it’s very early to say that. We need a proper diagnosis and then assess from there.’
With the transfer window closing on 1 February, Howe was not about to dive into the market as a result of Isak’s injury, nor is he keen to let anyone go.
Asked of possible departures, he said: ‘I don’t know. I don’t think so at this late stage. I’d be more than happy for the window to shut with no ins and outs.’
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