Hearts manager Craig Levein is worried about the severity of a knee injury picked up by Norwich City loanee Steven Naismith.

The forward hobbled off just eight minutes into yesterday's 3-0 defeat to Celtic in the Betfred Scottish League Cup semi-final at Murrayfield.

'He felt something in his knee,' Levein told the Scottish Daily Mail. 'It happened within five minutes of the game starting. He said he felt something go in his knee and he didn't know what it was.

'Obviously, he's had a couple of serious operations a while back, so he wasn't feeling too good about it.

'We need to get an investigation done so once we've done that we'll find out what the problem is.

'If Brendan (Rodgers, Celtic boss) was to have picked one Hearts player he could have taken off, then I'm sure he'd have picked Steven.'

Naismith has re-launched his career north of the border this season, after being deemed surplus to requirements at Carrow Road entering the final year of his current City deal.

The Scotland international failed to deliver following a big money move from Everton worth around £8million in January 2016 but has scored 13 goals in 20 games for club and country so far this season after joining Hearts for a second loan spell.

Naismith is free to talk to clubs early in the New Year as his deal expires next summer, and a Norwich return is not on the agenda.

Speaking to the Edinburgh News ahead of the game: 'I don't think so. As a club, they've moved on – and they're flying as well, which is good to see. There has been a big change there. I am, unfortunately, part of the past there.

'In the last week or so it's been more brought up (signing permanently for Hearts) but I've not thought about anything, even the fact that I'll be on a free transfer in the summer.

'I've loved the start of the season. I wouldn't rule it out at all. But I also know that this season, for me, is about my football – about playing and playing and playing.

'I'm not going to start doing things that will upset that one way or the other, whether that be with Hearts or whatever. Hearts have been great to me in the past year, 18 months come the end of the season. So that's something that I do appreciate. Journalists having been bringing my future up more. I've been playing well and not thinking about it.

'When you are on loan, you just think, 'Right, I'm on loan, enjoy.' There is an end point to that loan. My situation is slightly different in that I'll be out of contract, but I think everybody that's been involved in this loan is happy.'

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