Shaw suffered the problem moments before the break in Saturday's friendly with Real Sociedad, and Pochettino has revealed that it looks to be a ligament injury.
The 41-year-old told reporters: "In principle, it is his knee but we still need to know what the doctors will say.
"He has a problem in his ligament but we need to see what the doctors diagnose.
"We will have to see. He had to leave the stadium and the pitch and hopefully the problem is not as big as it looked and he will be okay."
The Saints withstood three equalisers from the Spanish side to win the match 4-3.