Thiago Silva's injury cast a large shadow over Paris Saint-Germain's 2-1 win over Napoli on Monday, according to coach Laurent Blanc.
Although the Ligue 1 season began on Friday for les Parisiens with a 2-2 draw at Stade de Reims, the reigning French champions visited the San Paolo on Monday for a friendly with Rafa Benitez's men, who do not start their Serie A campaign until August 31.
Goals from Zlatan Ibrahimovic and Javier Pastore ensured a slender victory for PSG but the withdrawal of captain Thiago Silva through a hamstring injury on 14 minutes - which reports have speculated could see the defender sidelined for six weeks - put a dampener on the evening.
"We will relish the victory because, even though it was a friendly game, we wanted to win," Blanc told reporters. "The shadow over the evening, though, is, of course, the injury to Thiago Silva.
"For now, we just know that he has a muscular problem - that much is obvious. The severity of the injury will be established after examinations.
"This sort of thing happens. He will be given the best care because we will need him."
PSG's two defensive summer signings, David Luiz and Serge Aurier, made their non-competitive debuts on Monday and Blanc was delighted with their showings, although the negative reception Edinson Cavani received at his former club disappointed him.
"For their first starts, David Luiz and Aurier were excellent," the Parc des Princes trainer added. "I am very happy with their performances.
"Regarding Cavani, when one returns to his former club sometimes one is not well received. It's a shame, but such is life.
"But now he will come back to PSG, and I hope the fans in PSG will make him feel at home again."
PSG face their first home game of the 2014-15 Ligue 1 campaign on Saturday against Bastia.