Who’s hurt and who’s surging? Four things to know about the Bucks.

Giannis Antetokounmpo (right) and the defending champion Bucks will pose a formidable threat for the Celtics in their second-round Eastern Conference series.Jonathan Daniel/Getty

The next opponent in the Celtics’ postseason run is officially set.

The defending champion Milwaukee Bucks eliminated the Chicago Bulls at home Wednesday night with a 116-100 victory in Game 5.

Game 1 between the Celtics and Bucks is scheduled to tip off at 1 p.m. on Sunday at TD Garden. The Celtics split their four-game regular-season series with the Bucks.

Some early observations:

1. Khris Middleton’s status is uncertain.

Middleton has been sidelined since spraining his MCL in the fourth quarter of Game 2 against Chicago. The Bucks announced after the injury that his status would be updated in approximately two weeks, which would be around May 4. At that point, the Celtics will have hosted Games 1 and 2.

On Thursday, the Athletic reported that Middleton will likely miss the full series.

During the regular season, Middleton averaged 32.4 minutes per game as a key contributor in Milwaukee’s offense alongside Giannis Antetokounmpo and Jrue Holiday. Middleton attempts the most 3-pointers on the Bucks and has been a particularly good shooter against the Celtics in the past. In two playoff series against Boston, Middleton has averaged 22.4 points per game on 51.6 percent shooting, both above his season averages.

When he last spoke about his injury on Friday, Middleton expressed his desire to be available for the second-round series.

“Hopefully, I’ll be ready or close to getting back to the court around then,” he said.

Will Milwaukee's Khris Middleton be able to face Boston?Morry Gash/Associated Press

The Bucks are also without veteran point guard George Hill, who sustained an abdominal sprain at the end of the regular season. Hill was initially considered day to day, but he ended up missing all of the series against Chicago.

“I think he’s going to need a little bit more time,” coach Mike Budenholzer said.

2. Grayson Allen is surging.

After Middleton’s injury, Allen emerged as a potentially reliable offensive option. Allen, who overlapped with Jayson Tatum for a season at Duke, made 11 of his 14 3-point attempts (78.6 percent) in Games 3 and 4 against the Bulls. While that rate is likely unsustainable, Allen’s contributions will be critical if Middleton remains unavailable.

“He’s kind of quiet, but confident,” said Budenholzer. “I think this is a confident group, a group that sees a player that can help them and appreciates his competitiveness. He’s just quiet, no [expletive], and comes to play. I think our guys gravitate toward that type of mentality. It’s certainly been a good fit.”

Allen has not been able to escape his controversial past, as Bulls fans relentlessly booed him throughout the series. In January, Allen was whistled for a flagrant foul on Bulls point guard Alex Caruso, who ended up missing two months because of a fractured wrist. Allen developed a reputation as a dirty player in college, when he was disciplined for multiple tripping incidents.

His Bucks teammates have embraced the boos, though, and even started to join in.

“We booed him during the game, and he really started hooping,” said Holiday.

What sort of role could Milwaukee's Grayson Allen have in the series?Morry Gash/Associated Press

Added Antetokounmpo, “Maybe we got to boo him even more. Maybe Milwaukee fans, we got to boo him ... Nah, we’re not going to do that.”

3. Milwaukee’s defense has been jiving.

The Celtics may have had the NBA’s best defensive rating of the regular season, but the Bucks own that honor in the postseason.

Headed into Wednesday’s Game 5, Milwaukee’s defensive rating of 94.2 was the top mark in the league by nearly 10 points. The Bucks have been dominant on the boards, boasting the most defensive rebounds per game (43.5) and highest defensive rebound percentage (80.9). They’ve also surrendered the fewest second-chance points (7.5) and points in the paint (33.5) per game.

Against Brooklyn, Boston’s offensive rating was an impressive 119.2, but the Celtics should have a tougher time against the Bucks. There are fewer obvious matchups for the Celtics to exploit.

Antetokounmpo and Holiday, who earned NBA All-Defense first-team honors last season, are the defensive cornerstones, but the Bucks have gotten contributions from nearly all members of the rotation. Point guard Jevon Carter, for example, has replaced Hill and recorded a stellar defensive rating of 82.7 in 14.5 reserve minutes per game.

4. The matchup decisions will be interesting to watch.

The Bucks have a big starting five, especially with Middleton out: Holiday, shooting guard Wesley Matthews, 6-foot-10-inch power forward Bobby Portis, Antetokounmpo, and 7-foot center Brook Lopez. Off the bench, their main contributors are Allen, Carter, and Pat Connaughton.

Several questions emerge. How will the Celtics combat Milwaukee’s size? If Middleton does not return, will the Bucks even want to roll out a starting lineup with that size? Perhaps Budenholzer will swap out Portis for Connaughton.

How will the Celtics contain Antetokounmpo? It will be a collective effort, but who will get the main minutes? When the teams played in the first round in 2018, Al Horford and Semi Ojeleye played crucial roles. But Antetokounmpo has since won a title and two MVP awards, so that task has only gotten more challenging.