The former £9million shotstopper has penned a new deal which will keep him at Parkhead until the summer of 2018.
And Deila says a pay-rise was necessary to keep the Scotland keeper from the clutches of English predators after he recorded his 30th clean sheet in 55 appearances for Celtic against Qarabag.
He admitted: “Craig came in here and he was not on the biggest salary. But he has done so good that we want to keep him for many years.
“We also give him something back for the hard work he has done, so it was positive for him and the club.”
Roy Keane paid a-then British transfer record fee to take him from Hearts to Sunderland and Deila believes the 31-year-old international is back in that kind of form.
He added: “Craig has done very well for us and will be very important for the future. It’s hard to say where he rates, but he’s played in England and did well.
“He is the best goalkeeper I have ever seen, so he’s at a high level. He’s a Premier League player, but how he compares to the best ones, I don’t know.
“Is he still worth £9million? For us he is.
“With his age now, his value may not be as high as before, but he might be even better than he was at that time.
“I can understand interest from England because he had a very good season last year and he will be even better this year as he’ll get a lot of matches played and more consistency.”
Gordon took over the No.1 spot when fans’ favourite Fraser Forster moved to Southampton in a £10million deal at the start of the last campaign and has been one of Celtic’s most consistent performers.