It's often claimed a player becomes far more valuable when they are out of the team – absence makes the heart grow fonder and all that.
Yet it's telling that this season Chelsea have managed to cement themselves in the Premier League top four and move to the summit of their Champions League group without the man many would consider their best player.
We are, of course, talking about N'Golo Kanté. The diminutive World Cup winner has started just five games for the Blues this season due to ankle and groin injuries, but Chelsea have not missed their midfield engine.
And that is largely because of Mateo Kovačić.
Frank Lampard has received deserved praise for his work with the club's young stars but there is an argument to be made that the improvement from players who were much maligned under Maurizio Sarri is his greatest achievement.
Last season, Jorginho was viewed as Sarri's on-field lieutenant. No matter the opposition, no matter the circumstances, no matter his form, the Italian international started. Eventually, that drew the ire of Blues fans.
Kovačić didn't fare much better. The Croatian had joined on loan from Real Madrid but looked nothing more than a jobbing Premier League midfielder. He was technically gifted and able to beat a man in limited space but offered very little in the way of game-defining moments before being substituted in the 60th minute for Ross Barkley.
For much of last season, Kovačić was a man without a defined position. That has changed under Lampard. The Chelsea boss has predominantly used the Croatian alongside Jorginnho in a 4-2-3-1 and has given the 25-year-old far greater licence to influence the game in the middle third.
No longer stuck in the rigidity of Sarri's 4-3-3, Kovačić has thrived. He is, as highlighted in the exclusive Football Whispers graphic below, making more passes, more forward passes, creating more big chances and completing more dribbles.
And the heatmaps show that while he is still predominantly operating on the left side of the pitch, he has more freedom to roam into central areas both in the defensive and attacking third.
“Kovačić's ability to play and then his ability to drive from midfield, that’s not the norm,” Lampard said after Chelsea's win at Watford.
“As a midfield player, it’s your worst nightmare having an opponent who can play and then drive by you out of nowhere. He was doing that today to great effect. I'm really pleased with him.”
In the Premier League this season, Kovačić has completed 26 dribbles. No Chelsea player can match that figure – Willian is second among the Blues squad with 16 – and only Aston Villa‘s John McGinn has completed more across the top flight (28).
But it's not just the offensive side of Kovačić's game Lampard has unlocked. The midfielder is also far more effective when the Blues do not have possession.
This season he is winning more tackles per 90 (1.93 compared to 1.50 last term), is making more interceptions per 90 (0.77 compared 0.41) and has won more defensive duels per 90 (8.22 compared to 6.71).
“I feel better and more confident than last year,” Kovačić admitted in August. “It makes me feel more relaxed as last year was difficult and I needed to prove myself.
“Last year was good, not perfect. This year I started well. I am missing some part of my game and I can improve and get better but I think it will come for sure.
“Lampard gives me more freedom and I can take the ball and go forward. I feel good. I have a good connection with the coach and all the team.”
The missing part of Kovačić's game? Goalscoring. January 29, 2017, remains the last time the Croatia international found the back of the net in club football.
Kovačić is in the team to facilitate those attackers. To win the ball back, break beyond a press and start an attack – against Watford, he had 157 touches, the most of any Premier League player in a single match this season.
It highlights how influential Kovačić has become. And when Kanté returns to full fitness, there is no guarantee he makes an immediate return to the starting XI.