CHESTER, Pa. – The Philadelphia Union will take the field for their first-ever MLS playoff game on Sunday at PPL Park. Union midfielder Veljko Paunović may not be as fortunate. Paunović, a longtime pro but a first-year MLS player, could be sidelined for the Union’s playoff opener against Houston in the first leg of the Eastern Conference semifinals (4 pm ET; ESPN2, ESPN Deportes). The 34-year-old Serbian is currently listed as doubtful on the club’s injury report with a right hamstring strain. "As of now, Veljko is training with us but not in full capacity," Union manager Peter Nowak said Wednesday from his weekly press conference. "With those kinds of injuries, you never know how it plays out. I don’t think it’s major enough to say he’s out the whole series." Before being sidelined for the Union’s loss in last Thursday’s regular-season finale to the Red Bulls, Paunović had started 12 of the club’s last 13 games, playing mainly as a withdrawn forward behind Sébastien Le Toux. If Paunović can’t go on Sunday, the Union could start the game with a five-man midfield like they did against New York last week, or partner Danny Mwanga – who is recovering from an injury himself – up top with Le Toux. Either way, Nowak believes Paunović’s absence would hurt the club. "In the stretch where we were playing good, he was an integral part of that," Nowak said. "So it’s definitely a loss in this capacity. He’s an experienced guy." The only other key player listed on the injury report for Philly is midfielder Justin Mapp (left quad strain), but Nowak said he should be fine for Sunday’s game. Mondragón feeling fine Since goalkeeper Faryd Mondragón returned to the lineup, the Union have yet to win and Mondragón has yet to record a shutout. But heading into the playoffs, Nowak is not the least bit worried about his club’s 40-year-old captain, despite the last two results of the regular season – a 1-1 tie to Toronto and a 1-0 loss to New York. "Faryd is an experienced guy," Nowak said. "The injury was just unfortunate. It’s not like he was sitting in front of the TV with a remote control and trying to flip channels [while he was hurt]. He was around us. He was part of the team, whatever we did." Nowak was also quick to point out the goals surrendered in each of the Union’s last two games were not a result of his injury or because the team had become more accustomed to rookie Zac MacMath, who had started the previous seven games in net. "I don’t think we had any problems with communication," the Union manager said. "I think he was very confident in those two games. The two goals, we should do better defensively not to put him in that position. I’m not worried." Nowak also isn’t worried how Mondragón will handle his first MLS Cup playoff contest, considering the veteran Colombian has played in numerous pressure-packed games during a two-decade career in South America and Europe. "This kind of stuff for him is not new," Nowak said.