Grayson's side have lost just once in 15 matches this season
Leeds manager Simon Grayson said too many of his fringe players failed to impress during their 2-1 Johnstone's Paint Trophy win against Darlington.
Grayson made six changes from the side that drew with Charlton on Saturday.
He told BBC Radio Leeds: "I'm happy that we've gone through but I'm not happy with how we played and the performance with it.
"A lot of players relaxed and didn't do themselves justice with their performances tonight."
Tresor Kandol made his first Leeds appearance in 17 months and scored their second goal after Andy Robinson - also recalled to the side - had given them the lead.
Aiden White and David Prutton started their first matches of the season while Lubomir Michalik and Mike Grella were also back in the starting XI.
But Grayson felt not enough of his players took their chance.
"I'm delighted we won the game but hugely disappointed with certain individuals and certain parts of the team tonight," he said.
"Regardless of me changing the team, it was an opportunity to go out and play in front of nearly 9,000 fans who've paid good money to come and watch us on a Tuesday night, and we should be going out and entertaining.
"I don't care if it's a JPT or Champions League game - I've got high standards and what I expect of my team and certain individuals didn't do that.
"Players get paid decent money to put in a performance and work hard and when you get an opportunity to come into the team then go and grasp it and make it hard for me to leave you out for future plans but not too many of them have done that tonight.
"I'm frustrated because we've got high standards and a lot of players have not reached them tonight."
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