The 23-year-old goalkeeper has a significant amount of scar tissue in the ankle he injured last season which is hindering his return to full fitness.
It is understood that Butland had a scan on Wednesday which showed plenty of scar tissue that is not allowing him to move freely.
If he is out for as long as the Potters fear, Butland could miss around six Premier League matches as well as World Cup qualifiers with England against Malta and Slovenia in October.
Butland, who fractured his ankle on international duty in March, posted an update on Twitter this morning:
Injury Update pic.twitter.com/BthIXDh2KS
— Jack Butland (@JackButland_One) September 2, 2016