Chris Chamberlain’s season-ending knee injury against Jacksonville on Friday turned out to be only the first in a spate of bad news for Saints' linebackers.

Interim coach Joe Vitt said Monday that starting MLB Curtis Lofton suffered a high ankle sprain against the Jaguars, and starting WLB David Hawthorne suffered a meniscus injury that will require surgery. Then about an hour after Vitt spoke, Lofton’s replacement, Ramon Humber, confirmed he has been suspended for the first three games for violating the NFL’s substance-abuse policy.

Vitt said Hawthorne was having surgery Monday and would miss “a couple of weeks.” He did not give a timetable for Lofton’s return, but high ankle sprains can linger long stretches of the season.

“It’s next-man up theory around here,” Vitt said. “This will be a great opportunity for Ramon Humber to step up. He’s been in our program and has played the position. He’ll have a great chance to show his skill level and what he can do.”

The problem for the Saints is Humber’s suspension, which had been mentioned on several Internet sites this summer but never confirmed until Humber talked Monday.

He said the suspension was for a “substance abuse” issue.

“It is what it is, but there are other guys who can get ready on this team,” Humber said.

Humber, entering his fourth year in the NFL, first signed with the Saints early in the 2011 season after being waived by the Indianapolis Colts. He played in three games for New Orleans in 2010 and 13 last year, when he made 21 tackles. They cut him just before the start of training camp this season, but re-signed him Aug. 6.

Vitt said Humber would start at MLB this Saturday against Houston in the Superdome.

“It’s all about trust,” Humber said. “I’ve been here before. They know what I’m capable of, and they believe I can step in and make plays for them.”

Jonathan Casillas will replace Hawthorne against the Texans, but Vitt did not rule out Hawthorne returning for the regular-season opener against Washington on Sept. 9.

“It’s speculation now,” Vitt said. “The diagnosis on David is encouraging. He hurt it early and continued to play on it, so he’s got a chance to be back for that game.”

“We’ll evaluate it,” he said. “I would probably say he’s out (for the Texans game), and we’ll evaluate it after that.”

Vitt said the Saints would look at potential trades for a LB but were happy with what they had.

Follow Saints reporter Guerry Smith on twitter @CBSSportsNFLNO.