Gordon Reid's arrival in South Africa yesterday to provide cover for Euan Murray completed a hat trick for Glasgow Warriors, as the club has now had an entire front row called into the Scotland squad over the past week.

The prop has been called in as Murray continues to suffer the effects of a hamstring injury.

Prop Jon Welsh was the first to be drafted after Ryan Grant had been called up by the British and Irish Lions in Australia. Rookie hooker Fraser Brown was next to be added to the squad, earning his place after Pat MacArthur suffered a knee injury. Reid's presence is, for the moment at least, purely precautionary, but he could find himself facing South Africa in Nelspruit on Saturday if Murray continues to struggle.

Earlier bulletins had suggested that Murray, the Worcester tighthead, had been making good progress but his problem recurred when he was put through a fitness test by land medical staff on Tuesday afternoon. The decision was then taken to call Reid in from pre-season training with Glasgow.

"Euan had an individual session with [Scotland physio] Stevie Mutch on Tuesday afternoon," said Gavin Scott, the Scotland team manager. "He had responded well to treatment but when he ran at about 70% effort he felt something wrong with his hamstring. It [Reid's presence] is precautionary, but that might change."

Despite the fact Scotland's front-row injury crisis was deepening, Reid had no inkling that he could be in line for a call-up. Having been told he had to get himself to South Africa, the 26-year-old dashed to his home in Ayr, gathered a few possessions together, said goodbye to his girlfriend and raced to catch a connecting flight to London. He arrived in South Africa barely 24 hours after being told he was needed.

"Gregor [Townsend, the Glasgow coach] brought the boys in, and I thought it was going to be bad news," said Reid with a smile. "Then he said he wanted to congratulate me for getting on to the Scotland tour."

Brown has also teamed up with the squad now. However, his prospects of making an improbable debut – his professional experience amounts to just four brief appearances as a replacement for Glasgow – appears to be receding as Steve Lawrie, the Edinburgh hooker whose back had been a cause for concern, is now reported to be much better.

Similarly, Tom Heathcote and Alex Dunbar are also recovering well from concussion. However, neither player is guaranteed a place in the side to be named today by Scott Johnson, the head coach, as he has made clear his intention to explore options in his selection.

Heyneke Meyer, the South Africa coach, made similar promises ahead of the Castle Lager Test series, but his team shows just two changes from that which defeated Italy. Ruan Pienaar and Marcell Coetzee replace Jano Vermaak and Francois Louw, respectively. Uncapped duo Siya Kolisi and Piet van Zyl have been chosen among the replacements.