Deila's side won 2-0 at Hampden Park the last time the teams met, when Kenny McDowell was in charge of Rangers.
The Glasgow rivals will meet again next month and Deila conceded there was now less between the teams.
"I think Rangers has been better than last year. You can see that their results are much better," said Deila.
"It's a game we really look forward to. It's going to be a big, big game and something to be happy for."
Rangers missed out on promotion after losing a play-off last season to Motherwell after finishing third.
Now, with Mark Warburton in charge, the Ibrox side have a 12-point lead over Hibernian at the top of the Scottish Championship.
Before facing Rangers, reigning champions Celtic have Premiership games to play as they look to protect a lead that has been cut to one point by Aberdeen.
"We have to focus on what's going on in the league now," Deila stressed. "There are five games before that game.
"So we are delighted and we will do everything to get the same result as we did last time."