France winger Lemar was one of the stars of Monaco's unlikely 2016-17 Ligue 1 title triumph but has found life tough since moving to Atleti two years ago.
The 24-year-old has not scored in 26 appearances across all competitions this season and has been an unused substitute in two of Atletico's four LaLiga games since the campaign resumed earlier this month.
His sole start during this period came against Real Valladolid, when he was substituted before Vitolo found a late winner.
Speaking ahead of Saturday's game against Deportivo Alaves at the Wanda Metropolitano, Simeone insisted he was satisfied with Lemar's performances in training but wants to see them replicated on a matchday.
"With Lemar we have tried and we continue trying to find a way that he can express on the field everything that excites us, from what we see in training," he said of a player he stated "hasn't been able to live up to expectations" earlier this year.
"We have shown him confidence, he has played important games and it will depend on what he manages to claim in his mind, in his inner strength.
"He knows that it depends on him because we have demonstrated that we have confidence in his football abilities."
Ten points from a possible 12 since the resumption have strengthened Atletico's hand in terms of qualifying for next season's Champions League.
They sit third, six points clear of Getafe in fifth with seven matches remaining.
However, the visit of 14th-placed Alaves should not necessarily be treated as a formality, given their habit of dropping points against teams in the lower reaches of the table this term.
"I do not find anything significant in that," Simeone countered.
"I do understand that in these games we could not be forceful and when you are not, the games are long and all the teams are competitive, whether they are down or up because they have important players."