Kroos said prior to Madrid's 2-0 defeat to Chelsea on Wednesday that he "never lost sleep" over an opponent during his illustrious 15-year career.
Mount made note of that remark after Chelsea advanced 3-1 on aggregate to set up a Champions League final showdown against Premier League rivals Manchester City.
"I saw one of their players say before that he doesn't lose sleep over individuals," Mount told CBS Sports.
"But I think as a team, they need to lose sleep over us as a team."
Kroos responded in a tweet on Thursday, paying a sharp-edged compliment in the process.
"Still sleeping ok. But well done yesterday. congrats," he tweeted.
"Good luck in your first CL final."
The allusion in Kroos' final sentence seemed clear enough.