Jesse Marsch issues update on nature of Leeds United double injury blow against Crystal Palace
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Both men were forced out of the Whites' final Australian tour game win the first half, Sinisterra with a hamstring problem and Forshaw with a knee issue.
Sinisterra was making his first start of pre-season but lasted just 12 minutes before being helped from the pitch by club doctor Rishi Dhand.
Forshaw went down after a slight coming together with Jean-Philippe Mateta but was able to jog off at Perth's Optus Stadium.
"Luis Sinisterra had a little hamstring injury, and we're hopeful that it's not too much and too long, too severe," said Marsch.
"So anytime we have a hamstring injury I'm totally dissatisfied because I think that's reflective of everything that we do with them physically. So we'll evaluate that and we hope that it's not so bad.
"Adam Forshaw felt Mateta kind of lean on him a little bit and tweaked his knee."We're hopeful as well that that one's not so bad, but we'll get more information in the next days."
Marsch was without captain Liam Cooper for all three games of the tour after the Scotland international picked up an Achilles injury on a treadmill during the summer.
Right-back Cody Drameh sat out the Palace game with a minor hamstring issue sustained in training, while Archie Gray was available again after being stretchered off against Aston Villa but Marsch left the 16-year-old on the bench in Perth