Telfer has spent his entire career in England

The 33-year-old signed a two-year contract in becoming Strachan's sixth summer capture, but it was unclear if he had been registered in time.

But Celtic said on Friday he would be able to play in Slovakia.

"I am delighted to sign with a club like Celtic at this stage in my career," said Telfer.

"I look forward to working with Gordon and Garry (Pendrey) again and hope to be part of a team which brings much success to Celtic and its supporters."

Strachan is still hopeful of adding to his squad further, but admitted that Telfer's versatility would prove valuable.

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"It's too late now to get anybody in for the first European games but I hope that we can do a bit more before the season starts," he added.

"We have tried to bring in young players but they cost money and like Adam (Virgo) he (Telfer) brings many options.

"They can play in many positions and that's what we need. This is a small squad and we need more quality, but those players can play in various positions."

As well as Virgo, Strachan has signed Artur Boruc, Maciej Zurawski, Jeremie Aliadiere and Mo Camara.