Joe Ledley has admitted the defeat to Rangers marked his most disappointing day for Celtic, but hopes to ease the pain by helping Wales beat England this weekend.
Neil Lennon's Bhoys missed out on Co-operative Insurance Cup glory after going down 2-1 to their Old Firm rivals on Sunday.
Ledley scored Celtic's goal but insists that gave him no comfort following such an agonising loss.
"We let ourselves and our families down. We're not happy," he told Celtic View.
"In the first half we did well but in the second half we lost our shape. On another day we might have won but we've got to try to move on now and win all our games.
"They didn't hurt us that much but we all know we can play better, we've proved it all season. We just didn't produce.
"We've just got to pick ourselves up and go again. It was the most disappointing day of my Celtic career."
Celtic lead the SPL title race by just two points, while Rangers have a game in hand, and Ledley knows the pressure will be on right to the wire.
"Every game from now on is going to be a tough one and like a final," he explained.
"We just have to go in there with confidence, play our own game and not focus on what they are doing.
"It's going to be tough and there will be injuries and suspensions. We just have to stick together as a group, move on and try to win as many games as we can."
Ledley is determined not to let the Celtic heartache affect his performance for Wales this Saturday, when England visit the Millennium Stadium.
The midfielder is looking forward to playing in front of a packed house and feels Gary Speed's Dragons can spring a surprise.
"It's like a local derby - the Welsh hate the English and the English probably hate the Welsh," he said.
"But it's going to be a good game to play in. All the players on both sides are going to be up for it. We just have to focus on ourselves.
"I have never played in the Millennium when it's been full but this one is going to be a sell-out and a great game.
"Hopefully we can get a result but England are a great team and have world-class players.
"It's going to be a great atmosphere, like you see in the rugby too, and it will be passionate. We all love playing for Wales and the fans love watching us play so hopefully we can put on a performance for them.
"I've played against a couple of Premier League players and have done pretty well so hopefully I can do so again if I play.
"You do want to play against the best players in the world and I have a good chance of showing I can do that. It will be a great honour to play against them.
"At the end of the day, it's what we do on the pitch and it's down to us now to start performing."