The Sweden international was stretchered off in the first-half of the Magpies’ 2-1 Carabao Cup win at Tranmere Rovers in midweek.
Howe revealed on Friday that the injury “didn’t look good” for Krafth, and it’s now been confirmed that the 28-year-old will be sidelined for “a number of months”
Speaking after the 1-1 draw at Wolverhampton Wanderers, Howe said: “It’s a massive blow for us.
“Emil has been superb for us on and off the pitch ever since I came to the football club in all sorts of ways, he’s a brilliant guy.
“We’re all really feeling for him at the moment. It’s an ACL injury, so he’ll be out for a number of months.”
Krafth, who stepped up superly in Kieran Trippier’s absence last season, has vowed to return “as soon as possible”.
Posting on Instagram, Krafth said: “Hard to find words and still can’t believe it. This was not the way I wanted the season to start!
“Gonna be out for several months with a knee injury. Devastated I can’t be out there and help the team, but I will do my best to push the lads to reach success!
“One thing I know is that the sun will rise tomorrow again and I will work extremely hard to get back as soon as possible!
“Thanks for all the messages and love you all have given me. See you soon back out there!”