Winger Emerton and midfielder Grella were both on Rovers’ books when Kean, 52, took charge in 2010 after the departure Sam Allardyce.
And both left a big impression on the Scotsman - 95-cap Emerton for his statistically confounding “Olympic cyclist-like” lung-busting durability.
Forty-six cap Grella, meanwhile, shocked Kean and with his innate ability and technical acumen.
Had Grella been fit for the 2011-2012 season, Kean believes Rovers might even have avoided dropping out of the Premier League after an 11-year run in the top flight.
Instead, an accursed injury run limited the former Empoli, Parma and Torino enforcer to just nine appearances in his final two seasons in Lancashire, and just 45 all up in four years.
Emerton, meanwhile, amassed 257 Premier League appearances in his eight years with the Blue and Whites, beguiling Kean with his otherworldly endurance levels.
“There’s only one other player I’ve ever encountered with a similar physical capacity, and that’s (Liverpool captain) Jordan Henderson,” said Kean.
“I’d put them right up there alongside each other.
“I remember saying to Brett one day, ‘I’ve never actually seen you out of breath’ and he replied, ‘I don’t ever get out of breath. I know when I’m struggling because my muscles start tingling’.
“I spoke to the club physio about it and he said when that happens it means you’ve got no glycogen left.”
Glycogen is a readily mobilised storage form of glucose - an energy source burned by the body.
“At one point they measured his lung capacity and Brett’s was comparable with an Olympic cyclist,” continued Kean.
“He was just blessed with a massive set of lungs that could carry him around the pitch.
“I’ve only seen Prozone (the player analytics tracking system) produce statistics like Brett’s with one other player and that was Jordan.”
Henderson came into Kean’s orbit during a loan spell at Coventry City, when Kean was assistant to Chris Coleman.
Kean also worked under the former Wales boss at Fulham and Real Sociedad.
“Jordan was on loan from Sunderland and also played wide right like Brett back then,” he said.
“They were both absolute machines. Sometimes you actually have to protect these types of players from themselves, otherwise they can run themselves into the ground.
“With Brett you could ask him to double up with your full-back and the next minute he was sprinting up the other end to cross the ball. It was astonishing to watch.
“He was a top pro - he never said much and was a quiet lad inside the changing room.
“He also had good technical ability and was a magnificent crosser of the ball. I think he also quite liked having defensive responsibilities and was brilliant without the ball as well.”
The pair’s association was cut short in 2011 when Emerton, now 41, requested a release to join hometown team Sydney FC as a marquee signing.
“I didn’t want him to leave the club but when he had the offer the club didn’t stand in his way because the people above said we had to get the wage bill down and he was on a decent salary,” added Kean.
“He was easily good enough at 32 to have stayed on in the Premier League.”
Kean, who was in the running for the Newcastle Jets job that went to Ernie Merrick in 2017, feels Grella’s time at the club was all about what might have been.
“Anytime he was fit he played,” he said. “For he, was far more than just a number six. He could start attacks off with penetrating passes and he could switch play at will.
“He could just sit in front of the centre-backs and he always wanted the ball and then he would get his head up and play a pass.
“Obviously his reputation in Italy was more as a destroyer who could break the game up. But he was an excellent footballer who was just unfortunate with injury.”
Those setbacks came in the form of calf, knee and groin issues, and prevented Grella ever getting up a head of steam.
“You know what it’s like - you get one injury and you want to rush back and then another one crops up. I think it was a really mentally difficult time for him,” added Kean.
“I think if he’d been fit during the final year of his contract we’d have picked up more points (and possibly even avoided the drop).
“He was vocal in a positive way inside the dressing room - he was terrific with younger players. A different character to Brett, very outgoing and upbeat. He was a captain type. Not that Brett was negative ... he was just more reserved.
“Vince was a much better player than I’d imagined.”
After resigning with Rovers third in the Championship, Kean went on to coach Brunei-based DPMM in Singapore’s S-League before quitting in 2017.
Lately, he’s been working for Greek Super League side OFI Crete as their director of recruitment, but should an A-League opportunity arise at some point, he’d be interested.
“100 per cent I’d be keen,” he said. “I’ve found Australian players very easy to work with and I’ve followed the game there. It’s a place I’d really like to work one day.”
