Boston Celtics center Kristaps Porzingis continues to battle side effects of the viral illness that first afflicted him in March, a source told Shams Charania of ESPN.

He suffered an energy crash just before Game 1 of his team's series against the New York Knicks on Monday, limiting him to 13 minutes of action. The sudden loss of energy is reportedly one of multiple side effects stemming from the ailment, which caused the Latvian to miss eight consecutive regular-season contests from late February to mid-March.

The 7-footer suited up for Game 2, but Al Horford replaced him in the Celtics' starting lineup. Porzingis played a team-low 14 minutes off the bench, finishing with eight points and four rebounds.

He didn't start Saturday's Game 3 either, but made his first appearance midway through the first quarter.

Porzingis has reportedly tried to alleviate the side effects by taking IV fluids and immune boosters, as well as altering his sleep patterns. The 29-year-old said in March that doctors couldn't identify the specific illness.

The Latvian felt he had turned a corner before the start of the playoffs, according to Charania. Porzingis played all five games of Boston's first-round series win over the Orlando Magic, averaging 27.4 minutes with 12 points and 5.8 rebounds per contest. However, he struggled with his shot in the series, shooting just 35.2% from the floor, including 2-of-17 (11.8%) from deep.