He officially arrived in the Spanish capital on July 27 for a fee of €60 million (£52.7m/$77.8m), less than a fortnight after being part of the 23-man France squad that had swept to World Cup success in Russia.
However, the versatile attacker, who is most noted for his performances on the left wing, had not simply emerged as a one-season wonder to hit such peaks.
Fees of up to €100m were bandied around the media on a dramatic summer deadline day in 2017. That very night Lemar made his international breakthrough by scoring twice in a 4-0 win over the Netherlands but his expected transfer to the Emirates never materialised.
Nevertheless, the switch to Atleti was expected to crown his ascent to the very top of the game but he has instead seen the upward momentum of his career grind to a halt.
Once described as having a “left foot like caviar” by former France international defender Bixente Lizarazu, the 24-year-old has served up only gruel at the Wanda Metropolitano.
Over the course of 17 months and 64 appearances, he has only three goals and six assists, none of which have come in 21 appearances in all competitions this term.
Now, Atletico Madrid head coach Diego Simeone appears to have lost patience with the Caen youth product.
Noted for his fierce on-field attitude as a player, the Argentine unsurprisingly tackled Lemar verbally in a similarly no-nonsense manner.
“Facts speak better than words,” Simeone grumbled in a press conference before a clash with Levante, which Lemar missed officially due to injury. "Lemar is an important player who hasn’t been able to develop his game but who has characteristics that other players don’t have.
“But, as a footballer, every time he has been available, he’s played a lot more than he hasn’t played. His characteristics have always excited me. But he hasn’t been able to live up to expectations.
“Today, who is to know if he will stay or not.”
As it stands, though, it seems likely that Lemar will be sent packing, perhaps even this month, having been already given ample opportunity to shine.
Premier League sides retain an interest in the forward, enticed by his undoubted potential, which he has only been able to show in tantalising glimpses while in the Spanish capital.
There has been little evidence, though, that the player who scored 14 and laid on another 18 during Monaco’s title-winning campaign in 2016-17 is about to re-emerge under Simeone.
Indeed, in 945 minutes of competitive action this season, he has only 0.6 expected goals and 0.8 expected assists. For a player who is supposed to act as a creative hub, these tallies are nothing short of pitiful.
What Lemar’s role with Atleti is supposed to be is somewhat unclear, and these muddied responsibilities seem to have seeped into his mindset, which on the field has regularly appeared confused.
The Madrid side often appear a team in need of a player to provide spark with a moment of brilliance or a touch of skill. This should fall right in the wheelhouse of Lemar but a lack of confidence has too often caused him to dither or misplace passes.
Citing Andres Iniesta as his role model, Lemar admitted during his rise with Monaco that he “tries to avoid duels and concentrate on passing and movement”.
This lack of natural aggression, one of the hallmarks of Simeone’s side, has not endeared him any further to the coach and a departure now seems the logical conclusion.
It has been quite a fall from grace for a player who was once billed by former Monaco team-mate Jemerson as a superior player to Kylian Mbappe.
“I like Lemar very much,” the defender told Goal in August 2018. “He is very good tactically. He defends, he attacks and he does everything. He is very important to our team and he played very, very well last season.
“When I arrived in Monaco, they talked a lot about him and I was very impressed. He has an incredible ability to dribble and shoot.
“It’s normal [Mbappe gets more coverage] because those who score more goals always do, but I really like Lemar.”
Such talent means there will be no shortage of suitors for the forward, who retains a price tag in the region of £50m, with Chelsea the latest club to be linked with him.
Tottenham’s interest, however, has been the most persistent, while Ligue 1 giants Lyon are reportedly seeking a loan deal in a bid to plug a gap left by injuries to Memphis Depay and Jeff Reine-Adelaide.
It is the Premier League, however, that is likeliest to provide the escape that Lemar seems to need in order to regain his best form.