The incident was sparked by a missed assignment by Thomas, he confirmed in an Instagram post in which he shared video of the play. He wrote: "Being sent home sucks. I can't take the reps I need to keep momentum going. But I can reflect on things and keep working my plan to help the team win."
He added: "A mental error on my part. A busted coverage that I tried to explain calmly [met] with built-up aggression turned into me getting into with a teammate."
He later deleted the post.
Thomas and Clark yelled at each other on the sideline and had to be restrained by teammates and coaches, with Thomas putting up his fists at one point.
It's unusual to see a heated argument like this between two players in the same position group.
Thomas was not present at Saturday's practice. Clark was practicing Saturday.
When asked about disciplinary action for Thomas, a source said the situation is "fluid."
"That's an organization decision that [head coach] John [Harbaugh] will address," Ravens assistant head coach David Culley said after Saturday's practice.
Harbaugh wasn't scheduled to talk Saturday, and he wasn't made available to reporters.
This is the second time Thomas, entering his second season with Baltimore, has had a confrontation with a Ravens teammate. Last year, Thomas had a heated exchange with nose tackle Brandon Williams after a game against Cleveland.
Thomas, a seven-time Pro Bowl safety, signed a four-year, $55 million deal with Baltimore in March 2019. His nine-year run in Seattle ended with him extending a middle finger to Seahawks coach Pete Carroll while being carted off the field with a leg injury.
Parting ways with Thomas, 31, would be financially difficult unless Baltimore can avoid paying his $10 million in guaranteed salary this season. If the Ravens released or traded Thomas, he would count $15 million against their salary cap this season as well as $10 million in dead money in 2021.
If the Ravens make a move with Thomas, DeShon Elliott would likely take his spot in the starting lineup. Ravens officials are high on Elliott, but the 2018 sixth-round pick has finished his two NFL seasons on injured reserve and has played in a total of six games.