Scott Lawson will join the Scotland squad that departs for South Africa on Friday after Ross Ford was ruled out through injury.
Ford suffered a calf injury on training on Wednesday and as a result the Edinburgh man will not take part in the Dark Blues' Tests against Italy, Samoa and their hosts the Springboks.
"Ross Ford pulled up in training in Aviemore on Wednesday," said Scotland interim boss Scott Johnson.
"He was scanned at Spire Murrayfield Hospital and a calf tear was diagnosed, recovery from which takes, on average, more than six weeks.
"It's unfortunate for Ross but, looking on the bright side, it will give him the chance to have an off-season, which can do him good.
"It also gives an opportunity to assess other players, which is one of the key things this tour is about.
"It's a time then for Scott and the two hookers already named in the tour party Pat MacArthur and Stevie Lawrie to compete for places."
Lawson, who will join Newcastle from London Irish next season, last turned out for Scotland in their humiliating loss to Tonga last November.