The 49ers plan to offer their vacant head-coaching position to Shanahan, according to multiple reports Tuesday.
"Kyle would be a big loss," Blank told ESPN on Wednesday. "But great coaches and great teams, that's what happens in the National Football League, unlike when I was running (Home Depot). When we had somebody who was ready to run a large division, it wasn't a problem. You'd take (him) and move him out of his division and give him his own division.
"In the NFL, you only have one NFL team. And unless we're going to put Kyle in charge of our soccer team -- and we already have a good coach there -- that's it. We only have one great football coach.
"Great coaches like Bill Belichick and Bill Parcells in the past, Coach (Joe) Gibbs and Andy Reid -- and the list goes on and on -- are great NFL coaches who have produced over time, and they lose their coordinators. Same with Mike Tomlin."
The 37-year-old Shanahan interviewed for head-coaching vacancies with the 49ers, Denver Broncos and Jacksonville Jaguars during the Falcons' playoff bye week. He can't come to an agreement with the 49ers until either after Sunday's NFC Championship Game against the Green Bay Packers with a loss or until after the Super Bowl.
If the Falcons advance, Shanahan can have a second interview with the 49ers between weeks of the NFC title game and Super Bowl LI, which will be played Feb. 5 at NRG Stadium in Houston.
"I think Kyle has focused hard on being inclusive this year (with) the other players and coaches," Blank told ESPN. "He's focused on that. He's focused on being a good listener and trying to understand where they were coming from. Kyle is a brilliant offensive mind and a great play-caller. Part of being good at any position of leadership in life is being a good listener and understanding where other people are coming from. That just makes you better. I think he got better this year in that regard. And I think he and Matt were more on the same page this year than they've been in the past."
Quinn was defensive coordinator of the Seahawks through the Super Bowl, while the Falcons held open their head-coaching job for him.
"I definitely have shared insight with him as he was going through the process," Quinn told reporters Wednesday but declined to offer more specifics about Shanahan's status.
Shanahan is in his second season as offensive coordinator with the Falcons, who averaged an NFL-best 33.8 points per game. He has also served as offensive coordinator with the Washington Redskins (2010-13) and Cleveland Browns (2014).
Shanahan is the son of longtime NFL coach Mike Shanahan.
San Francisco is looking for a new head coach for the third time in as many seasons, with Chip Kelly being fired after the team's dismal 2-14 campaign.