Brendan Rodgers thinks extending Craig Gordon's contract would be his best signing after the goalkeeper helped Celtic to a 1-0 victory over Aberdeen after Chelsea failed in a bid to sign him.
Gordon kept his seventh clean sheet in eight matches as Celtic went 25 points clear in the Ladbrokes Premiership title race thanks to Dedryck Boyata's 57th-minute header.
Celtic have a year's option on the 34-year-old when his contract expires this summer but a longer and better deal is in the offing.
"It was difficult for Craig because I don't think he is built for the stress," Rodgers said. "He is a big guy who is calm and laid back and it probably got on his nerves.
"But I have reassured him that he is an absolutely massive part of what I'm doing here.
"You see the level of his game, his composure, his quality, everything. And I'm very hopeful that soon we will tie him down for longer here because he is a huge player in relation to how I want my team to operate. That will be our best signing once that gets done."
Chelsea also have an interest in Moussa Dembele but Rodgers could afford to joke after the striker reaffirmed his commitment to Celtic after travelling to London for a deadline-day scan on a knee injury.
Rodgers said: "We had to make sure the physio didn't lose sight of him down there.
"Ironically the hospital he was in was in Chelsea, believe it or not. So I said to Tim (Williamson), be like Franco Baresi and just stay tight to him.
"But he was happy to come back. He is loving it here. He got some fluid out of his knee, he has had a good reaction to it, so we will see how he is for the weekend."
Celtic - who were without the injured Leigh Griffiths as well as Dembele - initially struggled to break Aberdeen down but Boyata headed home Scott Sinclair's free-kick and they never looked like losing their lead.
Rodgers hailed Boyata after his second winner in only his fifth game of the season.
"Outstanding again, and he deserves all the credit because it has been a difficult period for him since he first came in from Manchester City with expectations," Rodgers said.
"But he has really worked hard over the last three months since he came back fit and he has just had to stay patient.
"A wonderful guy, he understands exactly what I am looking for from a centre-half: first and foremost to defend. He is aggressive, wins his duels in the air and he is comfortable on the ball. The message is just play simple.
"And then in the box he is a huge threat - he looks like he will score every time he is in the box. It was a good header and he defended well when he had to.
"He got good applause at the end from supporters and deservedly man of the match."
Aberdeen manager Derek McInnes was frustrated at the manner of the goal after denying the hosts a shot on target from open play until the game opened up following Boyata's header.
"We are disappointed, angry that we haven't taken something from the game," McInnes said. "I don't think we did enough in the final bit to get any more than a point but I thought we were worthy of a point.
"We tried to contain them, pressed them, showed good tenacity in the challenge. Our pressing game was excellent, Celtic never got into any real rhythm or any progressive passing that they are so good at.
"We did so much right so to lose from a set-play, which wasn't a free-kick, having seen it again Kieran Tierney has slipped. But a combination of that decision, the quality of Sinclair's delivery, and us not getting tight enough to Boyata means that goal has separated the teams."