Simmons left in the third quarter of the Sooners' 33-7 victory over Baylor last week, hopping toward the sideline before trainers met him and helped him the rest of the way off the field.
Stoops refused to say how long Simmons will be out.
However, Stoops says Ryan Broyles, the Sooners' leading receiver, returned to practice and "there's a chance he could play" Saturday in Dallas.
Broyles missed last week's game because of a hairline fracture in his left shoulder blade the previous week in the Sooners' 21-20 loss at Miami.
He had been expected to miss 2-to-4 weeks.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
NORMAN, Okla. (AP) _ Oklahoma coach Bob Stoops says leading receiver Ryan Broyles "has not been ruled out" for No. 20 Oklahoma's game Saturday against No. 3 Texas.
Broyles missed last week's game against Baylor after suffering a hairline fracture in his left shoulder blade the previous week in the Sooners' 21-20 loss at Miami.
He had been expected to miss two to four weeks because of the injury.
Even after missing most of the past two games, Broyles leads Oklahoma with 23 catches for 346 yards and seven touchdowns this season.