Rousseau led the ACC in sacks last season with 15.5 and is widely considered a first-round selection in the 2021 NFL draft. ESPN's Mel Kiper Jr. lists Rousseau as his No. 24 overall prospect and the top defensive end.
Diaz was holding a news conference via Zoom on Thursday in advance of Miami's first practice and opened by saying he expected all players would be available, but shortly before ending the meeting, he announced he'd just received word of Rousseau's decision.
"We've had a great relationship with Greg," Diaz said. "He's an outstanding young man and we want to thank him for everything he's done. We want to support him any way we can as he looks to achieve his dreams of playing in the National Football League."
Rousseau, a 6-foot-7, 253-pound junior, had 54 tackles, 19.5 for a loss, and seven quarterback hurries last season, his first year of significant playing time.
"We're for these young men. We're advocates for them," Diaz said. "We want what's best for them, and if this is what he's chosen, we're going to support him. Our guys, it'll be next man up, and I'm sure they'll be supportive of Greg's decision as well."