That would make it almost impossible for Lucas to play for Michigan State against Northern Iowa in the Midwest Regional semifinals this week.
Lucas was injured late in the first half of the Spartans' 85-83 victory over Maryland on Sunday.
"It looks like it might be a torn Achilles, to be honest with you," Izzo said moments after the Spartans advanced thanks to a 3-pointer at the buzzer by Korie Lucious, Lucas' replacement.
"That poor kid, he was devastated," Izzo said. "It's a shame for him. But it's part of athletics and we're just going to have to move on."
Izzo added that the diagnosis was not definite because Lucas had yet to have an X-ray or MRI on his left leg, "but the prognosis is 85 percent of that."
A somber Lucas was less forthcoming while sitting in a jubilant locker room minutes before Izzo spoke.
"I will get X-rays [Monday] and probably will know more then," Lucas said, speaking barely above a whisper.
He scored a career-high 25 points in the first-round over New Mexico State.
Lucas began hopping on one leg and keeping his left foot off the ground after making a runner and landing awkwardly on his left leg near the baseline with 2:28 remaining in the first half. It was his only field goal in four shots. He had six assists and one turnover in 16 minutes.
"I just came down the wrong way," he said.
He said the pain was more in his leg than in his foot or ankle.
As play continued at the other end, Lucas hopped down court on his right leg while wincing in pain. He tried to defend the ball before officials gave him an injury timeout.
The junior then hopped to his bench. After a trainer looked at his lower left leg for a moment, Lucas hobbled into a tunnel that leads to the locker room.
Three-point specialist Chris Allen did not start and played just 4 minutes for the Spartans because of an injury to the arch in his right foot sustained late in Friday's win. He entered midway through the first half, moved stiffly for a couple of minutes, then left the game and remained on the bench except for a brief entry late.
He says he will try to play on Friday against Northern Iowa in St. Louis.
"I've got a week to get ready," Allen said. "I'm about to be in the training room all day, every day. I might sleep in there."
Michigan State led by nine points when Lucas left. He remained out at the start of the second half, and wasn't even on the bench until 12½ minutes remained in the game. The Spartans' lead had grown to 15 by then, thanks to the shooting of Durrell Summers. Then came the Terrapins' frantic rally.
On the bench during the second half, Lucas wore a hooded sweatshirt and sweat pants, plus the walking boot on his left foot and ankle. He was the only player not in the massive pile of Spartans that squashed Lucious at the opposite end of the court following the sophomore fill-in's winning shot.
Lucas hopped over to coach Tom Izzo near midcourt instead.
"I told Coach Iz I loved him," Lucas said with a small smile. "He said the same back to me."