"He's going through a really tough time," Fisher said Thursday. "He lost his mom Tuesday, and ... it was sudden. It was unexpected so we got him to the airport Tuesday afternoon and communicated with him last night.
"As you can understand, it's very, very difficult."
Nora Lee Cooper Witherspoon was 56.
The Titans said Wednesday that Witherspoon had been excused from practice for personal reasons.
Fisher said the Titans are leaving it up to Witherspoon when to return to the team, though the veteran told the coach he plans to be back for Sunday's opener against Oakland. Coaches are getting information to the veteran going into his ninth NFL season.
"He'll be back for the game. At that point, we'll evaluate it," Fisher said. "He expressed 100 percent interest and confidence in his ability to play in this game. Fortunately for Will, he's a very experienced player."
The Titans signed Witherspoon in March to a three-year, $11 million contract, making him their first signing of free agency. He has been working with middle linebacker Stephen Tulloch to anchor a unit that has veteran David Thornton on the reserve/physically-unable-to-perform list healing up his hip and Gerald McRath suspended for the first four games.
If Witherspoon isn't able to play, that would stress an already thin unit. Colin Allred worked with the first-team unit through the preseason but has been limited this week by an ankle.
"If this unfortunate tragic circumstance had happened to a younger player, there'd really be no way for the player to come back and play missing the time," Fisher said. "In Will's case, I have confidence we're communicating with him over the next couple days ... When he can come back, we'll get him back."
Tulloch said he spoke with Witherspoon by telephone before his teammate caught his flight at the airport.
"For her to be fairly young with no health problems, it is shocking to him. ... Your heart goes out to him," Tulloch said. "Football comes secondary to your family.
"When he comes back, we'll be here for him."