Rasmus Sandin, selected No. 29 by the Maple Leafs in the 2018 NHL Draft, also played for Keefe with the Marlies. The only healthy defenseman on the Maple Leafs roster who didn't is Tyson Barrie, who was acquired in a trade from the Colorado Avalanche on July 1.
Keefe will need to hope that the familiarity between he and those defensemen will help compensate their lack of experience heading into their game against the Florida Panthers on Thursday (7 p.m. ET; TVAS, FS-F, TSN4, NHL.TV), one Dermott calls the Maple Leafs' "biggest game of the year."
Barrie has played 548 career NHL games, 52 more than the combined number played by Marincin (222), Dermott (151), Holl (75), Sandin (24), Rosen (16) and Liljegren (eight). Muzzin (579), Rielly (516) and Ceci (494) have combined for 1,589 career games.
"There are a lot of familiar faces back there. It's pretty darn close to the Calder Cup championship defense," Keefe said. "That's a good thing. It's a good thing for me in the confidence and comfort in those guys.
"These guys are not AHL defensemen (any more). That's the big thing."
Keefe acknowledged the group will be tested, starting with the game against the Panthers. Toronto (33-23-8) is third in the Atlantic Division, two points ahead of Florida.
"It's not ideal but it's part of the gig, right," Keefe said. "It's the reason why you develop players, it's the reason you acquire depth, it's the reason you strive for a good and healthy minor league system. It's so when these situations happen, you can press on.
"We've done it before. Rielly, Ceci, [Muzzin], they've all been hurt at various times this season. You just have to find a way to get points."
The Maple Leafs, wanting to maintain stability, opted not to trade Barrie before the NHL Trade Deadline on Monday, despite a number of inquiries. Toronto's lone move was acquiring Rosen from the Colorado Avalanche for goalie Michael Hutchinson.
"Imagine if we didn't have (Barrie) or Calle both," Dermott said. "Fortunately, things played out the way they did and we do.
"Now it's time to show what we can do."