Last week Pardew declared the player to be "50/50" in his bid to be fit for a place in Chris Coleman's Wales squad and the manager told a news conference a member of Palace's medical staff will go the extra mile to ensure the 29-year-old makes it to France.
"We have a full roster, other than Joe Ledley," the manager said. "He would have been in the frame [to face United]. It's a terrible shame to miss him.
"When the Welsh team meet up, our physio will go across with them and Joe.
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"That should give him a fighting chance for the Euros.
Coleman also remains optimistic Ledley can be a part of Wales' first appearance in the finals of a major tournament since the 1958 World Cup.
He told Sky Sports: "Joe deserves to go because the kid is a top, top advert [for the game], also because he's earned it. He deserves it because he's a good player and an important player.
"We will wait until the last possible moment to make a decision. I'm optimistic and I'm hopeful. But with injuries you never know.
"We had [Wolves midfielder] Dave Edwards, who had an injury after Christmas and got back four weeks earlier than scheduled. What an incredible athletic Dave is.
"Sometimes injuries last longer, so we just have to wait and see, weigh everything up."