The defender was carried off in the first half of last Thursday's 3-3 draw against Newcastle at St James' Park after landing awkwardly.
There was some hope Long, who was making his first Premier League appearance, had avoided serious injury but scans confirmed the club's worst fears with the 24-year-old now facing a lengthy period on the sidelines.
"We didn't think it was a good incident when we saw it," Dyche said.
"Obviously it is a blow to him. He got 20 minutes of Premier League football. It's what football sometimes throws at you."
In more positive news for the club, striker Sam Vokes has enjoyed a good return from the same injury after scoring against Tottenham in the FA Cup on Monday, and Dyche hopes he can lend Long his support through his recovery.
"It's positive for Longy that he's got somebody who's just been through it, someone to talk him through it and he knows he's got a support system in place that will get him through it," Dyche said.
