United have been linked with a host of targets throughout this summer transfer window, but routinely with the Leicester City centre-back. And with the window closing in little more than a week, time is running out to complete a deal for the 26-year-old, who the Foxes value at £90 million.
However, United and Maguire both feel that Leicester's valuation is pricing the player out of a move, with the United hierarchy having offered £70m and sources at the club telling ESPN FC that they are unwilling to meet Leicester's valuation.
Speaking to ESPN FC in an exclusive interview from Orlando ahead of his participation in Wednesday's MLS All-Star Game against Atletico Madrid, Rooney said that Maguire would be "a good signing" for his former side.
"I think Harry's a good player and over the last few years he's improved as a player," the D.C. United captain said. "He's gotten better, and he's been a main player for Leicester City, but also for England.
"I think he'd be a good signing if they can get him."
The other transfer saga looming over Old Trafford is the future of Paul Pogba.
The 26-year-old said last month that he was ready for "a new challenge somewhere else." Earlier this month, his agent Mino Raiola said that he was "in the process" of negotiating his client's exit from the club.
Pogba has been linked with a move to Real Madrid or Juventus since the spring, and reports in Spain have suggested that Los Blancos are prepared to step up their interest in the midfielder amid an abject preseason tour of the U.S.
Rooney was diplomatic when asked about whether United should hold on to Pogba, suggesting that there are several factors at play regarding his potential sale.
"It's obviously down to the club, to the board, to the manager, but I think also to the player," Rooney told ESPN FC. "If the player wants to stay, he'll stay and prove what a good player he is.
"Behind the scenes, I'm sure they're working on whether to keep him or whether to let him go."