The Scotland keeper's signing on a two-year contract - he is Ronny Deila's only recruit to date - was considered an insurance policy by the Hoops in case Forster moves back to England.
With Southampton ready to come back in with an improved offer after their initial bid failed to match Celtic's valuation, the anticipated race to buy the England squad goalie is set to move into top gear.
Deila has made it clear he wants Forster to stay as he is a very important player in the team he has inherited from Neil Lennon. But if the value Celtic have placed on the 26-year-old is met, a move back to England appears inevitable to enable Forster to mount a serious challenge to Joe Hart to become the national team's No.1
At 31, and having proved his fitness again after more than two years out following knee surgery, Gordon would appear a ready-made replacement
But the man who has been Forster's shadow for the past four years, Lukasz Zaluska, is not prepared to sit back and watch Gordon leapfrog him.
And, as he prepares to return to Poland this week for Celtic's Champions League third qualifying round tie against Legia Warsaw, Zaluska made it clear he is set to dig in.
Zaluska was on the bench as Forster recorded another two clean sheets in the qualifiers against KR Reykjavik, while Gordon watched from the stand.
The Pole is ready to leap into action if Forster does move out, and said: "In the two games against Reykjavik, I was on the bench while Fraser was playing.
"But maybe he'll change clubs. Southampton sent an offer, supposedly £7.5million, but our bosses rejected it.
"If Fraser leaves, I'd be fighting for the place with Craig Gordon. But the club may bring in another goalkeeper."
The signing deadline for the third qualifying round ties passed last night, though clubs can add one more player up to 24 hours before the first leg kick-off.
Deila, who has taken his squad to Germany today for a friendly against St Pauli, is more concerned about retaining what he has, with Virgil van Dijk also the subject of interest from unprompted suitors.
Hamburg and Sunderland now appear to be the clubs leading the charge for the Dutch defender, with Southampton also linked, though no concrete offer has yet been received.