Just as the Orioles were finally finding a starting rotation worthy of their playoff aspirations, injuries have jeopardized that push at the worst possible time.

Manager Buck Showalter said Dylan Bundy will start the home regular-season finale Sunday against the Arizona Diamondbacks, and right-hander Kevin Gausman has been pushed back to Tuesday night at the earliest with what Showalter called the beginnings of an intercostal muscle problem in his rib cage.

“We're hoping he's our starting pitcher Tuesday or Wednesday,” Showalter said of Gausman. “That's what we're hoping for. But it won't be Sunday. We've got the off-day there to play with. We'll see how things manage the next few days. He felt a little bit the start of an intercostal. We think we caught it in time, but we'll see how it manages.”

Gausman started feeling the problem during his start Tuesday night against the Boston Red Sox, when a three-run home run by David Ortiz in the seventh inning went a long way toward spoiling what was looking to be another front-line start for him. Even with it, Gausman has a 2.94 ERA since the All-Star break and is pitching like the top-of-the-rotation starter the Orioles have needed for years.

Ortiz given dugout phone, donation: As part of their pregame tribute to retiring Red Sox designated hitter David Ortiz ahead of his final game at Camden Yards on Thursday night, the Orioles tried to strike a fun tone by invoking their common enemy as well as making reference to the smashed dugout phone from 2013.

The ceremony featured a video package of all the home runs Ortiz hit against the New York Yankees. Ortiz smiled through that one but didn't seem amused by the second video package — a full clip of him smashing a dugout phone after a strikeout on July 27, 2013, at Camden Yards.

Ortiz didn't turn and watch the video, but he smiled when Orioles center fielder Adam Jones trotted out of the dugout with the remains of that phone mounted on a plaque and authenticated.

Additionally, the Orioles made a $10,000 donation in the name of Ortiz to the World Pediatric Project, which helps critically ill children in the Dominican Republic.

Showalter promotes 5K: For the sixth year, Showalter and his wife, Angela, will host the KidsPeace Halloween-themed Trick-or-Trot 5K Race and 1-mile walk benefit Oct. 29 starting at 8 a.m.

Proceeds for the event, which begins and ends at Camden Yards, will go to KidsPeace Maryland Foster Care and Community Programs and the charity's KEYS (KidsPeace Empowering Youth to Succeed) program, which helps youth make the transition when they can no longer be in a foster home when they turn 21.

“The fans have been so great to show up,” Angela Showalter said. “[The kids] were sharing about one of our youth last year who was just emotionally taken aback that these people all came out for her. And here's a child who doesn't have family, but a bunch of Orioles fans came out to support her. And that was a very touching thing. And that might be enough to carry her to go on through life.”

Around the horn: Showalter said he expects the Orioles to be well-represented on the rosters of next spring's World Baseball Classic, and somewhat begrudgingly gave the players his blessing to represent their countries. “It's something that people think is important, and I can see why. So we'll cooperate, as usual,” Showalter said. Third baseman Manny Machado is the only confirmed player participating so far, after he announced earlier this year that he'll play for the Dominican Republic. … Gausman and his fiancee, Taylor North, presented a check for $31,776 to the Baton Rouge Area Foundation, the results of a fundraiser to support the region after last month's floods. … Left-hander Jayson Aquino was unavailable Wednesday and Thursday with a viral infection, Showalter said.

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Baltimore Sun reporter Eduardo A. Encina contributed to this article.