Ross County boss John Hughes feels Celtic have rediscovered their mojo – with Scott Brown directing the music.
Club captain Brown has had less game time than usual in recent months but impressed Hughes during Celtic's victory over St Johnstone last weekend.
The midfielder also helped Celtic see out their fifth-consecutive win on Wednesday when he replaced Ismaila Soro for the last 20 minutes of a 1-0 victory over Aberdeen.
County host Celtic on Sunday and Hughes expects as tough a challenge as ever against the Scottish Premiership champions, who began the weekend 15 points adrift of leaders Rangers.
"They have got their mojo back after the sticky period they had," the former Celtic defender said.
"They play some great football. I was waxing lyrical about Rangers and their performance against us at Ibrox and yet when you look at Celtic, albeit Rangers beat them, in the Old Firm game Celtic were the better football team.
"So we know the strength of the opponent and they seem to have got that hunger back."
County fell to the bottom of the table after their game against Hibernian was postponed last weekend and Hughes wants his players to approach Sunday's challenge with enthusiasm.
"You want to test yourself against the best as a player so it has to inspire you and you have to look forward to it," he said.
"They have got some fantastic footballers, and I just keep laughing at all the speculation about Scott Brown.
"He was playing there against St Johnstone and he was the playmaker. He was orchestrating the band and just keeping it ticking over, making it simple.
"So we know what we are up against – a team I have so much respect for.
"We will need to be at our maximum, every one of our players, will need to be at our best, full-out, to beat Celtic.
"It's up to us to come up with a game plan, really try to stifle Celtic, but also try and take the game to them and let them know they have been in a game."
