Messi played no part in either of Argentina's games during the international break due to a minor hamstring injury, sitting out a 2-0 defeat of Italy and a 6-1 thrashing at the hands of Spain.
"We do not know too much about the physical condition of Messi and Ter Stegen," Valverde said on Wednesday.
"This Thursday they will undergo medical tests to assess their status.
"I'm calm about Messi's injury. Tomorrow we will see how he feels.
"Messi finished the last game with Athletic Bilbao well, it is true that he had a little trouble, but it was nothing important. I still do not know what we are going to do, we think and hope it is not important.
"We are not going to worry before time, when the doctors see him we will decide the steps to follow, but we think it is not important.
"We will play in all of the competitions this month and we will see how the players are when they return from international duty. The three points against Sevilla can be quite decisive."