Matt Phillips is the latest winger to pull out of the Scotland squad ahead of the friendlies against the United States and Norway.
The Scottish Football Association confirmed the QPR player had withdrawn through injury on their official Twitter account.
Gary Mackay-Steven and Craig Conway were called up earlier in the week after wide men James Forrest and Chris Burke pulled out.
Phillips, who has two caps, was recalled to the squad after missing the finale to Scotland's World Cup qualifying campaign following a broken arm.
Scotland manager Gordon Strachan called up in-form Leeds forward Ross McCormack on Wednesday night after Blackburn striker Jordan Rhodes pulled out with a training-ground knock.
McCormack has scored six goals in two games for Leeds and was initially omitted as Strachan sought to have a look at the likes of Phillips.
Phillips pulled out with a hamstring problem while Rhodes rolled his ankle during a training session.
Strachan revealed on Thursday lunchtime that Blackpool goalkeeper Matt Gilks, Derby midfielder Craig Bryson and Watford wide player Ikechi Anya all sat out training on Thursday but no decision has been made on their fitness ahead of Friday night's Hampden clash with the States.
Strachan is looking forward to testing his rejuvenated team against a side who have qualified for their seventh consecutive World Cup finals.
The Scotland boss said: "I hope it will be a good one, they will be hoping it is a good one as well.
"They are 13th in the world. We have put on a friendly we think is attractive to the fans and the players of both sides, we think it is well worth their journey to get here and well worth us getting together.
"We are feeling quite good about ourselves and I'm sure they will be feeling good about themselves at the moment.
"It is always a result thing in our business but performance as well, and we can work on other things this week towards our long-term future as a group, so that has been good."
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