The NFL player's attorneys were in court Wednesday over a separate matter in the DUI crash case ... when the judge presiding over the hearing said Ruggs did not properly submit a breath test earlier this month.

As part of the conditions of Ruggs' release ... the 22-year-old must submit to alcohol testing several times a day -- but the judge said he missed one of his required check-ins.

Ruggs' attorney, David Chesnoff, acknowledged the missed test ... but added that Ruggs had "self-tested" just minutes later.

"He's been dutiful," Chesnoff said. "Completely dutiful."

The judge didn't seem to care much though ... responding, "It doesn't matter. He still missed it so I would like to see your client."

The proceedings next Monday will be the first time Ruggs has been seen in public since he was in court on Nov. 3 -- the day after he crashed his Corvette into another car in Las Vegas, killing a woman and her dog.

At that hearing, in which Ruggs posted bond and was released from custody, the football player showed up in a wheelchair while wearing a neck brace.

As we previously reported, Ruggs has been hit with 5 charges -- including four felonies -- after authorities say he was drunk and speeding just before the fatal crash.