Calem Nieuwenhof's ascension to become a key first-team player at Heart of Midlothian will mean he is set to miss out on the AFC U-23 Asian Cup next month.

The midfielder would be in line to be included in Tony Vidmar's squad for the tournament which doubles up as qualification for the Olympics. However, the competition clashes with Hearts' final pre-split league encounter against Livingston and the Scottish Cup semi-final against Rangers.

Hearts are not duty-bound to release the 23-year-old.

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"I'm not sure," Naismith said when asked if Nieuwenhof would be allowed to go to the tournament.

"We'd have too many big games coming up at that point. He's been valuable for us. I'm not sure that's something we could sanction, really."

Naismith believes Nieuwenhof would have been in line for a call-up to Graham Arnold's Australia squad for a World Cup qualifying double header with Lebanon if it wasn't for the hamstring injury sustained in the win over Celtic. The midfielder missed the two games before the international break but is expected to return for the Kilmarnock clash at Tynecastle Park a week on Saturday.

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"I think he would have been," the Hearts head coach said. "I've said it for the last month. I think Airdrie in the cup was the first time I mentioned it - I think he'll make a squad within the season.

"From the moment he's come in as a regular in our team, he's been the most consistent performer. I think it's a matter of time. He's got so much quality. He's taken his time to settle in and I think the Australian national team know him from the youth set-ups. Tony Vidmar has come to see him throughout the season and even the conversations with him were that he was one of the ones pinpointed to be next in.

"It's unfortunate that he's injured because I think he would have made this squad. I think it's a matter of time."