Union coach Jim Curtin was optimistic about the return of two attacking players, Fabian Herbers and Sebastien Le Toux, for Saturday's key Major League Soccer match at Talen Energy Stadium against D.C. United.

Despite the optimism, neither has been cleared to play.

Herbers has a strained right hamstring that kept him out of both the June 29 U.S. Open Cup win over the New York Red Bulls and Saturday's 1-0 MLS loss at Houston.

Le Toux suffered a concussion in the Open Cup win over the Red Bulls and was sidelined Saturday against Houston.

Curtin said the team's training staff put Herbers through some rigorous tests on his hamstring on Tuesday.

"We knew it was a minor tweak, and it looks like he will be available for the weekend," Curtin said.

As for Le Toux, Curtin said he passed the first round of the concussion protocol testing and was able to run on Tuesday.

"He is going through the heading portion of the testing [Wednesday], and then he would be ready for the weekend. But that would be up for the doctors to decide when he can take that next step now," Curtin said.

The Union will be without defender Josh Yaro, who received two yellow cards and a subsequent red in the 87th minute during the loss at Houston. The second yellow was questionable as it appeared that Houston's Mauro Manatos flopped and sold the tripping call.

"I personally didn't feel it was a foul, but then again I am not in charge of the game," Yaro said. "It is [the referee's] decision, and there is nothing I can do about it."

mnarducci@phillynews.com

@sjnard