The 31-year-old has not played a football match for over two years after leaving Sunderland in the summer of 2012.
He had signed for the Black Cats for a record £9m from Hearts in 2007 but only returned to training last year after overcoming chronic knee problems.
Gordon spent time with Rangers getting fit but, now back to full fitness, Scottish champions Celtic are ready to sign him on a two-year deal - amid claims their current number one Fraser Forster is set to be sold.
Bhoys boss Deila did not comment on Forster's situation, with Atletico Madrid reportedly keen, but confirmed he was close to finalising a deal with Gordon.
"We are getting closer with Craig Gordon, it is down to the small details. We can make this happen but it's not confirmed yet," he told the Daily Record.
"We need to have alternatives. You always make contingency plans.
"If you are going to bring in older players then they need to have the right mentality and Craig has that."