Louisville opened fall camp on Friday without senior wide receiver Jaylen Smith, who underwent an emergency appendectomy earlier in the day, the school announced.
Smith, an All-Atlantic Coast Conference first-team selection last season, will be out for an undermined period, according to the university statement.
"We are fortunate to catch this early and anticipate a full recovery," head coach Bobby Petrino said. "Jaylen is doing well and we look forward to him returning to the practice field as soon as possible."
Quarterback Jawon Pass is replacing Heisman Trophy-winner Lamar Jackson this season and Smith is expected to be his top receiver, and possibly the Cardinals' No. 1 offensive weapon.
Jackson caught 60 passes for 980 yards and seven touchdowns in 10 games last season, and for his career he has 116 catches for 1,955 yards and 14 scores.