"We need competition for spots, we need to increase our base," Scott Johnson said at the Six Nations launch on Wednesday. "We can't be at the whims of injuries." Whim is the word. It was a couple of days earlier Johnson learned that his tighthead prop, Euan Murray, had cut his thumb while chopping wood during a team-building exercise and will be out until at least late February.

At the same time, Geoff Cross, Johnson's second choice in the position, has been struggling to get past Willem Nel into the Edinburgh team. The South African is in the middle of a three-year residency period to qualify for Scotland just in time for the 2015 World Cup.

By then Vern Cotter will be head coach while Johnson, who is serving in the interim, moves up to director of rugby. At that point, he will be happy to have Nel around, because his job will be to increase the pool of players Cotter has to pick from in 2015. But right now, Johnson has to steer the team through the 2014 Six Nations and Nel's success is making his life a little harder.

"Without Euan, Moray Low and Geoff have got to stand up," Johnson says. "We can't be dependent on one person. This is about the growth of this team. So we're going to find out about them, and that's the way it is."

In certain areas, Johnson is blessed. The back row and the centres, where he feels Matt Scott – "a prodigious talent" – and Alex Dunbar create "a formidable" partnership. "Some wonder whether Scott is ready," said Johnson. "He hasn't played since he fractured his hand against Japan last autumn. I wouldn't put him on if there was any doubt of him going the distance. There's a bigger picture here, too. I am trying to get sustainable combinations together in that position."

A family matter has kept Cotter from joining up with the Scots for the Six Nations but the two are in "constant dialogue". Johnson also says that he will still be involved with coaching the team when Cotter finally starts. "I love coaching blokes and I love being involved with the team, and that's what I will continue to do. Nothing really changes, the only difference is the press don't have to put up with me and I don't have to put up with the press. And I probably don't have to wear the tie as often. So there are a lot of benefits to it."