Frank Lampard will be like the Ghost of Christmas Past to Jose Mourinho when he takes his place in the Old Trafford dug-out on Tuesday for Derby County's Carabao Cup tie at Manchester United.
Lampard, 40, is setting out on his own managerial career with the Championship club. The former Chelsea and England midfielder has a made a decent start to his new job, with the Rams sitting in a playoff spot following five wins in nine league games.
Mourinho, whose first spell in charge at Chelsea coincided with the best days of Lampard's playing career at Stamford Bridge, will relish the challenge of putting his protege in his place by guiding United to victory.
But the presence of Lampard will also offer the Portuguese a reminder of just why he was so successful at Chelsea, and why he is finding it so difficult to replicate that winning formula at Old Trafford.
Few players embodied the best of Mourinho quite like Lampard. Think of Chelsea's back-to-back Premier League titles under Mourinho in 2005 and 2006 and the image of Lampard scoring, or celebrating, a crucial goal is an indelible one.
He hit 13 goals in Chelsea's first title season and 16 the following year, missing just three games over the two campaigns.
Mourinho's success has always been driven by hungry, committed, powerful players and Lampard ticked every box.
He also bought into his manager's methods and demands and became a better player for it, as did teammates such as John Terry, Michael Essien, Joe Cole, Didier Drogba and Ashley Cole.
When Mourinho looks around the United dressing room before kick-off on Tuesday night, he will not see a Lampard or a Terry or even a Cole.
Paul Pogba might be there, but although he arguably possesses greater talent than Lampard, there is no debate as to which one Mourinho would rather have in his midfield at United.
The same could apply to Cole and Anthony Martial -- both talented players, but only Cole displayed the readiness to embrace Mourinho's tough love and demand for improvement and work ethic.
Whether Mourinho was an easier manager to succeed under back in his Chelsea days is a fair question to ask, because he certainly displayed more charisma back then and the kind of Pied Piper personality which ensured that determined young players would follow his path.
But it also requires the players to possess the same will to win and improve that the likes of Lampard, Terry & Co. had in abundance under Mourinho at Chelsea.
At United, Mourinho is not blessed with the same depth of quality and personality that he had at Chelsea. He inherited some of his best and most consistent players from Claudio Ranieri, but he also recruited brilliantly to make Chelsea a formidable outfit in his first two years at the club.
Mourinho has not been so fortunate at Old Trafford. Louis van Gaal built an imbalanced squad which was low on confidence, but Mourinho's signings have not had the desired effect, with Pogba one of the biggest disappointments, Henrikh Mkhitaryan sold within 18 months and question marks still hanging over the likes of Victor Lindelof and Eric Bailly.
His failure to make United competitive again -- truly competitive, as potential Premier League or Champions League winners -- has led to a debate over whether or not he is still one of the world's greatest coaches.
But it might just be as simple as accepting that he does not have the players that he had at Chelsea.
If that first title-winning team of 2004-05 was dropped into today's Premier League, it is safe to suggest that it would push Manchester City and Liverpool all the way simply because of the quality within the squad.
There would be no raised eyebrows over Mourinho's tactics because a team with a spine of Petr Cech, Terry and Ricardo Carvalho, Claude Makelele, Lampard and Drogba, would be a match for any of today's best sides.
But Mourinho does not have the luxury of such quality at Old Trafford and he certainly doesn't have a Lampard.
Maybe his best team-talk on Tuesday would involve showing a highlights video of that Chelsea team to the players in his United squad.
If Pogba was locked in a room for 20 minutes and forced to watch Lampard at his best, the France international might realise that he can deliver so much more for his team and become the player that his ability demands.
It would be wishful thinking on Mourinho's part, though, and the sight of Lampard sitting a few yards to his left will drive that home to him.
Lampard is a reminder of how it used to be and the frustration for Mourinho will be in the realisation that he doesn't have enough Frank Lampards in his United squad.