MIAMI — Jonas Valanciunas, who’s been so big for Toronto in the post-season, was on his way to what might have been one of the biggest games of his career Saturday night when he crumpled to the floor in agony.

The Raptors are about to find out just how big he was.

Valanciunas has been ruled out of the Eastern Conference semifinal against the Miami Heat with a sprained ankle.

"Big, big, big, big, big blow for us," Raptors general manager Masai Ujiri said Sunday. "Big blow for JV. … But you know what? This is the life in the NBA and we carry on."

Valanciunas was averaging 15 points, 12.1 rebounds and 1.4 blocks in 10 playoff games this season.

Through three games of this series, he averaged 18.3 points and 12.7 boards, and he already had 16 points and 12 boards when he limped to the locker-room in the third quarter Saturday — just a day after his 24th birthday.

"He’s been playing so well," Toronto guard Kyle Lowry said. "He was hitting such a great peak right now. His confidence was sky-high. But for us as a team, it’s next man up."

Raptors coach Dwane Casey said he didn’t think the ankle injury was severe until the medical staff informed him he was out for the game.

"He’s a tough kid… but once he didn’t come back I knew it was (serious), because he’s usually ‘Tape me up Tyler, get back in there’ type of kid," Casey said.

"Jonas was getting better every game at doing something, whether playing with confidence, screening properly, defending his position, doing a better job in the pick and roll defensive schemes. He was growing and it’s unfortunate because I thought (Saturday) night was going to be one of his best performances."

The complexion of the series changed Saturday night when both teams lost their starting centres. Valanciunas’ injury happened when he came down awkwardly on his ankle while defending a Dwyane Wade shot. The Heat’s Hassan Whiteside sprained his knee when he got tangled up with Lowry.

The severity of Whiteside’s knee injury isn’t known. The team has listed Whiteside as day to day.

Valanciunas missed 22 games in the regular season with a broken hand, and the Raptors went 16-6 in his absence.

Bismack Biyombo should see significant minutes with Valanciunas out, and was the last Raptor off the practice court Sunday as he worked on his shooting.

"Biz gives us a shot-blocker, an elite shot-blocker, a guy who can run the floor extremely well, he can roll," Lowry said.

But no-one was sugar-coating Valanciunas’s loss Sunday. Toronto outscored Miami by 41 points when Valanciunas was on the floor in the first three games. The Heat have outscored the Raptors by 39 when he hasn’t been on the court.

"Jonas, he does a lot for us," Toronto’s DeMarre Carroll said. "He gives us extra opportunities, you can’t take that away from him. Next guy has to step up. This league is about opportunities. A lot of guys complain, claim they don’t get opportunities. This is a prime example of getting an opportunity on the biggest stage."

Lowry’s emergence Saturday night was welcome news among the bad. Lowry, whose shooting had been woeful in the post-season, scored 29 of his 33 points in the second half of Saturday’s win as the Raptors took a 2-1 series lead.

"It’s fantastic for us," Ujiri said. "I think him and DeMar (DeRozan), they’ve struggled but we’re winning, we’re still alive, and that says a lot about them and they keep fighting and fighting and I think (Saturday) it really showed.

"So we’ll keep fighting and the guys are extremely confident… (Lowry and DeRozan) helped us get to where we are so we’ll live and die with them."

Heat coach Erik Spoelstra believes the series will be competitive no matter who is or isn’t playing.

"It’s 287-285," Spoelstra said. "Every game has gone down to the final possessions, two overtime games."

Game 4 is Monday in Miami, then the series returns to Toronto for Game 5 on Wednesday.