CHESTER, Pa. – If the Philadelphia Union hope to get back into the playoff picture and return to the US Open Cup final, they’re going to have to do so without one of their top players.

Central midfielder Vincent Nogueira, who had been in the midst of perhaps his best stretch with the Union, pulled his right quad after entering in the 80th minute of Sunday’s 3-2 loss at D.C. United and revealed following Wednesday’s training session that he’ll be out of commission until at least the end of August.

“It’s a bad thing for me,” Nogueira said. “I started to feel very healthy and it was a very good thing to be on the field, and now I have to stop for three weeks.”

Nogueira has battled some injury issues since coming to Philly before the 2014 season, but when he’s in form, the Union insist he’s one of the league’s most underrated players.

And he was certainly in form over the last couple of months, scoring four goals since the last week of May – including two in a 3-0 rout of the Portland Timbers on July 11 – and carrying the Union on his back during their 10-man triumph over the New York Red Bulls last week in the US Open Cup quarterfinals.

That makes this injury pill even tougher for Union head coach Jim Curtin to swallow.

“To lose Vincent is a big loss for us,” Curtin said. “He was in the form we saw last year when he was kind of flying. His fitness was good. And it was just a play where he swung at a ball and he felt his quad go.”

Curtin knew right away the injury wasn’t minor when Nogueira couldn’t run during the final 10 minutes of the game in D.C., which also hurt the Union’s chances of pulling out a result at RFK Stadium.

But the long-term ramifications are much more troubling for the Union, who are in danger of completely falling out of the playoff picture if they don't quickly string together some solid results.

“We know that August is very important – we play a lot of important games against teams for the playoff race,” Nogueira said. “It’s never a good moment. But actually this is the worst moment of the season [to be out].”

Curtin didn’t reveal how he’d replace the Frenchman in the lineup, but Zach Pfeffer or new signing Tranquillo Barnetta are the most logical replacements to slide into Nogueira’s box-to-box midfield role.

No matter what the Union coach does, though, overcoming the 27-year-old’s absence will be difficult. When Nogueira starts, the Union are 6-6-4 with a +1 goal difference; when he comes off the bench or isn’t used, Philadelphia is 0-6-0, getting outscored 16-6 in the process.

“It’s a very harmful injury,” Curtin said. “Difficult news. But we have no time to feel sorry. It’s going to be a good New York team that comes in and we have to have someone step into that spot.”

Dave Zeitlin covers the Union for MLSsoccer.com. Email him at djzeitlin@gmail.com.