Pender will miss the Seminoles' upcoming game against Wake Forest on Saturday.
A 21-year-old redshirt junior from Fort Myers, Florida, Pender lightly bumped into an offensive lineman Tuesday during practice, causing his lung to collapse. Fisher originally hoped Pender would be released from the hospital Thursday.
"He's still in the hospital, I believe getting out today or tomorrow hopefully," Fisher said Monday. "I'm not a doctor, but his lung was fine, but it still had just a little bit it needed to inflate back to, and [doctors] were waiting for that to fill up."
Dalvin Cook's primary backup, Pender, is second on the Seminoles with 140 rushing yards this season.
Fisher is unsure whether Pender will miss the Oct. 10 game against rival Miami, which like No. 11 Florida State is undefeated. The game against the Hurricanes begins a tough six-game stretch that also includes Louisville, Georgia Tech, Syracuse, Clemson and NC State.
Against Wake Forest, Fisher said sophomore Johnathan Vickers and freshman Jacques Patrick will relieve Cook. The 6-foot-1, 226-pound Vickers and 6-foot-2, 235-pound Patrick have combined for 37 yards from scrimmage this season, but Fisher said the two have practiced alongside Cook and Pender all year. Patrick enrolled in January.
"Big, physical fast guys that bring it downhill and are hard to tackle," Fisher said of Vickers and Patrick. "Catch the ball well, pass protect well, bigger bodies that are athletic. Like I've said all along, I really like those guys."