The trade-deadline push came early for the Cubs when an injury to All-Star catcher Willson Contreras prompted them to deal for Royals catcher Martin Maldonado as their 6-3 loss to the Reds ended Monday.

The Cubs sent left-hander Mike Montgomery, who got the final out of their historic World Series victory in 2016, for Maldonado.

The news was surprising on multiple levels, especially given that manager Joe Maddon pronounced Contreras healthy before the game and said he would start Tuesday. But an MRI exam on Contreras’ right foot, which sidelined him Sunday, revealed a strain of the arch muscle on the inside of the foot, team president Theo Epstein said.

‘‘Our medical staff feels like if he were to try to play on it that he could be risking exacerbating the injury and turning it into something long-term,’’ Epstein said. ‘‘We don’t expect it to be longer than the 10 days. That’s what we hope for, anyway.’’

Contreras, who said he was fine before the game, declined to talk to media afterward.

Right-hander Kyle Hendricks said Contreras looked fine but appreciated the cautious approach for one of the top-hitting catchers in baseball.

‘‘The way he’s been swinging it and what he’s done for this team, we’re going to need him down the stretch,’’ Hendricks said.

Whether the move signals an aggressive approach to trades as the Cubs try to win a wide-open National League this season, it was at least a proactive move for a 10-day injury. It also kept Maldonado, a highly rated receiver, from being traded to a rival and added a pitch-framing skill missing at the highest levels among Cubs catchers.

‘‘They had been talking to a couple of teams about Maldonado; we knew that,’’ said Epstein, who indicated the Cubs and Royals already had been working on a version of the deal before they worked quickly to close it once Contreras was headed to the IL. ‘‘He’s an established catcher in this league who does a lot of great things behind the plate.’’

Maldonado spent five seasons with the NL Central rival Brewers before spending the last 2½ seasons with the Angels, Astros and Royals.

‘‘He can really receive,’’ Epstein said. ‘‘He can really throw. He’s caught playoff games. He’s a favorite for pitchers to throw to. He calls a great game. He has really soft hands. And he has a lot of experience and savvy.’’

Montgomery, who has struggled through the worst season of his career, was a savior for the rotation in 2018, when he made 19 starts and produced a 3.69 ERA while filling in for injured starters. In the end, however, he had no role on the Cubs.

For him, the trade means a chance to become a regular starter. He already has been told he’ll start Friday for the Royals. For the Cubs, it means another member of the 2016 World Series team is gone.

‘‘Obviously, you can’t talk about his contribution without talking about getting the last out in that World Series that changed everybody’s life,’’ said Epstein, who acquired Montgomery from the Mariners a few months before his 10th-inning relief appearance in Game 7 in Cleveland.

‘‘It’s bittersweet, for sure,’’ said Montgomery, who earned his first career save in the World Series clincher. ‘‘You get those emotions going through your head, and you understand what kind of impact you had on a lot of people’s lives here. Now I’m going to look forward to a new opportunity. . . .

‘‘The game’s a business, and it’s just how it works sometimes.’’