Scotland's front five options are likely to be reduced significantly for Saturday's match against Tonga, with Richie Gray struggling to prove his fitness, while Allan Jacobsen is expected to quit the international game.

Jacobsen missed Saturday's meeting with South Africa after withdrawing from the squad for what were described as "personal reasons" and it is understood the 34-year-old has decided that his international career, which began with a tour of New Zealand in 2000, is over. Gray, meanwhile, faces a week of tests if he is to prove his fitness for the trip to Pittodrie on Saturday.

It was confirmed yesterday that the 23-year-old lock, generally considered the best player in the Scotland squad, suffered concussion early in Saturday's meeting with South Africa at Murrayfield.

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"Richie will now be subject to the return-to-play protocol following a concussive episode," said James Robson, the team doctor.

Where that would once have led to Gray being automatically sidelined for three weeks, modern practices mean that if he remains symptom free as his exercise regime increases this week he could still face the hard-hitting South Sea Islanders.

As he battles to prove his fitness there have been increasing calls for more of his former Glasgow Warriors clubmates to be brought into the Scotland team.

One of the most curious aspects of the autumn has been that, with Matt Taylor working successfully on defence with both Warriors and Scotland, national head coach Andy Robinson has mainly stuck with players he previously worked with at Edinburgh.

The capital side has lost its last seven matches, largely because they have been falling off tackles – just as Scotland did against New Zealand and South Africa, whereas Al Kellock, Glasgow's captain, who came off the bench to replace Gray on Saturday, has been delighted with the impact youngsters from his club have made.

"I'm so, so happy for Henry [Pyrgos] and so, so happy for him last week as well," he said of the player who scored Scotland's only try on Saturday. "He's such a good character and he's worked incredibly hard. He's not number one with us [at Glasgow]. He knows Chris Cusiter's there, but whenever anything's asked of him he's done it. The same is true of Pete Murchie.

"Pete has done brilliantly this year and deserved to get on the bench yesterday. He'll be gutted that he didn't get on but it's a big positive, the number of these Glasgow boys that are pushing through, which makes me feel very happy and very proud.

"I don't know what [Robinson] will do but I'm hoping Pete will get a bit of game time next week because it's probably the hardest thing when you get that close but don't quite get on."