Harry Kane and Harry Winks have withdrawn from the England squad to face Germany and Brazil with Jake Livermore called up to the group.
Winks, who excelled on his international debut against Lithuania last month, has dropped out due to an ankle ligament injury.
But it is the withdrawal of Kane that will come as the biggest blow to Southgate going into the forthcoming prestige friendlies.
Kane, who is favourite to become permanent England captain, has scored seven goals in his last six internationals and is one of only a handful of players guaranteed to start in Russia next summer.