The Celtics will be without starting big man Kristaps Porzingis as they look to close out the Miami Heat on Wednesday.

Boston ruled Porzingis out for Game 5 of the first-round playoff series at TD Garden as he recovers from the calf injury that knocked him out of Game 4.

The injury is a right soleus strain, according to the team. Giannis Antetokounmpo suffered the same injury in his left calf during a game against the Celtics on April 10, and the Milwaukee Bucks star has not played since.

The exact timetable for Porzingis’ return is unclear, but he’s likely to miss at least the start of the second round, assuming Boston defeats Miami and advances. The top-seeded C’s would face the winner of Orlando-Cleveland if they can finish the Heat, who trail 3-1 in the best-of-seven series.

ESPN’s Adrian Wojnarowski reported Porzingis “is expected to miss a minimum of several games.”

Porzingis sat out 25 games during the regular season with various lower-body ailments, so the Celtics are accustomed to playing without the 7-foot-2 Latvian. Boston was 21-4 without Porzingis in the lineup.

“We’re going to have to play different, but next-man-up mentality,” Jayson Tatum told reporters after Game 4. “… Just next man up and find a way to win the game.”

Al Horford — Boston’s sixth man when the team is at full strength — likely will slot into the starting lineup in place of Porzingis, and reserve bigs like Luke Kornet and Xavier Tillman could take on larger roles off the bench.

Kornet, who missed Games 1 and 2 with a calf injury, has played just eight minutes this postseason, and trade-deadline pickup Tillman has yet to make his Celtics playoff debut. Nor has 7-foot center Neemias Queta, who split his time between Boston and the G-League this season.

The 37-year-old Horford played 34 minutes Wednesday night, finishing with seven points and eight rebounds.

The Heat will be down not just one, but several key players for Wednesday night’s potential series clincher. In addition to starters Jimmy Butler and Terry Rozier, who have yet to play in the playoffs, Miami also ruled out rookie forward Jaime Jaquez Jr., who suffered a hip injury in Game 4.

Boston shouldn’t need Porzingis to eliminate the shorthanded Heat, but his availability will be a major storyline as the playoffs progress.