Carroll also expressed optimism that the 64th overall pick in the 2019 draft will recover quickly and be ready to play Week 1.
Metcalf reportedly suffered the injury late last week. He didn't suit up Sunday versus the Minnesota Vikings.
Carroll said Metcalf underwent an MRI, which gave the team a clear look at the injury, although the coach didn't provide additional details about the nature of the ailment.
The explosive Metcalf wowed at the scouting combine, posting top-five scores among receiver prospects in the 40-yard dash, bench press, vertical jump, and broad jump - scores that were considerably more impressive considering his 6-foot-3, 228-pounds frame.
However, a poor score in the three-cone drill prompted some concerns about his lateral agility, which may have contributed to his slide to the second round of the draft.