Liverpool loanee in training ground bust-up
Leto, on loan from Liverpool, had been left out of the Athens derby against Panathinaikos on Sunday for a previous incident and, according to Greek media reports, was reluctant to perform his exercises along with the rest of the team on Monday.
"During yesterday's training session there was an issue with footballer Sebastian Leto who for the umpteenth time gave in to disciplinary problems forcing me to send him to the dressing room," Valverde said in a statement on the Olympiakos website on Tuesday.
"For this specific incident I have informed the administrative section of the club which is there to deal with it. As I have said in the past, for me the top priority is discipline and the calmness of the team which comes above all of us."
Leto, 22, joined Olympiakos in August on a season-long loan after failing to secure a work permit that would allow him to play in the UK.