Both players require surgery but Warriors coach and future Scotland supremo Gregor Townsend admits he is relieved the news is not worse.
Utility man Horne and wing Hughes were both stretchered off during Warriors’ narrow Guinness Pro12 defeat by Munster last Friday night.
Horne could be out for as long as four months with an ankle injury, while Hughes faces an eight-week lay-off with a knee problem.
But Townsend confessed he was worried the pair would be ruled out for longer.
He said: “It’s a blow. We knew it was going to be disappointing news given the way the injuries were at the weekend.
“But they are actually not as bad as some of our worst fears.
“Peter has had a really serious ACL knee injury in the past but that is fine and Rory’s is not as bad as we feared either.
“These are two of our hardest working players and we know they will work hard on their rehab to make sure they can come back as quickly as possible.”
Horne - who featured as a replacement during all three of Scotland’s three autumn Tests - is now likely to miss all of the RBS Six Nations campaign, although Townsend has refused to count him out of the later stages of the championship.
He said: “Peter was involved in all three games for Scotland during November, covering at stand-off and at centre, and he’s been excellent for us.
“It doesn’t rule him out of the entire Six Nations and he will have a target to come back at some point during that period.”