A 2-0 defeat to Serbia on Tuesday night officially ended hopes of booking a place at Brazil in 2014, as Gordon Strachan's men became the first European nation to have their fate sealed. The Scots have so far failed to secure a victory in a dismal campaign, which has seen them collect just two points from six games.
Home and away meetings with Croatia, as well as the visit of Belgium and a trip to Macedonia, still lie ahead, and Naismith told BBC Scotland: "We've got very tough games but the players are playing for their future international careers."
He added: "I said earlier in the week that I think we've got to grow up in terms of digging in and being mature about when we need to sit in and soak up the pressure and when we need to expand and try to go for the goals.
"As players, that's what you need to do or you're going to find yourself out of the national team."
Despite further defeats, against Wales and Serbia, Naismith disagreed with former Wales winger Mickey Thomas' claim that the current crop of players are the "worst Scotland team ever".
The forward said: "The statistics don't lie but I think we are a better team than what he was saying. To be honest, I don't think too many in the dressing room are paying too much attention to what a Welshman is saying about the Scottish national team."
A second-half double by striker Filip Duricic sunk the Scots on a depressing night in Novi Sad.
Naismith said: "In terms of overall play, it was a hard night on the pitch. Both teams did as well as they could, the difference was in both boxes.
"We didn't take our chances and we probably gave up easier goals than we would like to be conceding."
- Sports & Recreation