Aberdeen boss Stephen Glass revealed he was forced to take skipper Scott Brown off against Celtic due to cramp.
The 36-year-old was influential in the heart of midfield but was forced to leave the field in the 72nd minute against his former club.
The game was level at 1-1 when Brown, who won 21 trophies during his time at Celtic, left the pitch.
Celtic would go on to score a late winner via Jota.
Aberdeen have now failed to win in nine games and have taken just two points from the last 18 in the Premiership.
Ideally Glass wanted skipper Brown to play the entire 90 minutes but had no option but take him off when he cramped up – with Dylan McGeouch replacing him.
Glass said: “Scott cramped up.
“The pitch was a wee bit softer than it has been.”
Brown was facing his former club for the first time since joining Aberdeen on a two-year deal in the summer.
Former Scotland international Brown led Celtic to nine-in-a-row and an historic quadruple treble.
Celtic were desperate to retain their influential captain but he opted to join Glass at Pittodrie in a player-coach dual role.
Brown came close to netting against his former club with a bullet header from a Calvin Ramsay corner kick but the midfielder’s effort was saved by Celtic keeper Joe Hart.
🎙️ "Well that would have been quite something, a Scott Brown goal against Celtic!"
Scott Brown has just come off but almost put Aberdeen ahead against his former club. Will there be a winner?
📺 Watch the final 15 minutes of Aberdeen vs Celtic live on Sky Sports Football pic.twitter.com/9HZezMxajS
— Sky Sports Scotland (@ScotlandSky) October 3, 2021
Glass reckons the emotions of facing his former club could also have affected Brown.
He said: “I said to him it was probably the emotion of the week.
“You don’t actually realise it but you would be an alien if that didn’t affect him.”