WASHINGTON -- Reinforcements are en route.

The Cardinals, besieged by injuries at the outset of the 2021 season, will welcome back a trio of familiar faces over the span of the next several weeks. The first is Tyler O’Neill, who's slated to be activated off the injured list when the Cardinals return home on Friday, manager Mike Shildt said prior to Monday’s series opener against the Nationals

“We’ll try to get those guys back, but we also appreciate what we have in the moment and making the best of what this team’s bringing,” Shildt said. “We're doing a good job of that.”

It never hurts to have options, though.

Here’s a look at the three ailing Cardinals, where they stand in their rehabs and when each might return, or in two cases, debut:

Player: OF Tyler O’Neill

Injury: Right groin strain

Estimated return: Friday

O’Neill tweaked his groin on an awkward swing before sprinting out of the box on April 10 against Milwaukee. Now, he’s progressing his running to full speed and has hit a pair of home runs in recent sim games, Shildt said. Though he’s eligible to come off the injured list on Wednesday, the Cardinals will give him an extra day to recover with Thursday’s scheduled off-day and have circled Friday’s series opener against the Reds.

It’ll mark the return of a rough season so far for O’Neill, who absolutely raked in Spring Training but has gone 4-for-28 with 14 strikeouts across eight games.

Player: OF Harrison Bader

Injury: Right forearm strain

Estimated return: Early May

Monday was a momentous day for Bader, who took live batting practice for the first time since going down with the forearm strain and receiving a platelet-rich plasma injection in the last week of Spring Training. Bader has also progressed to throwing from 120 feet and is recovering well from each session.

His return will hopefully normalize what’s been a wonky start for the outfield defense so far this season, which was anticipated to be a strong suit for an already staunchly defensive team.

“Texted him last night, and he's excited and feels good,” Shildt said. “Not going to rush to get back, [but] excited to get back.”

Player: RHP Miles Mikolas

Injury: Right shoulder discomfort

Estimated return: Late May

Mikolas hit a milestone recently as well, facing live hitters for the first time since Feb. 25 on Sunday. Mikolas, who missed all of last season with surgery to repair the flexor tendon in his right forearm, said he went too full-throttle in his first bullpen session during Spring Training, which led to the shoulder discomfort.

Mikolas has been limited to fastballs and changeups -- namely, not the more torque-inducing breaking balls -- so far in his ramp-up. Shildt said it would be fair to compare Mikolas’ current status as the equivalent of a pitcher in late February, meaning it could be more time before he returns to the Majors. Next on the docket is working in breaking balls into a batting practice session, then some simulated game action.

Everyday they’re shufflin’

Off an uneven weekend in Philadelphia and facing a Nationals starter who utterly dominated them last time out, the Cardinals shifted their lineup to open Monday’s series in D.C., most notably elevating Dylan Carlson to the No. 5 spot and dropping Matt Carpenter to No. 7.

The moves were twofold -- Carpenter, hitting just .069 (2-for-29) to open the season, hasn’t exactly warranted the at-bats towards the top of the lineup, while Carlson (.868 OPS) has. And the Cardinals sought to throw a new-look lineup at Joe Ross, who twirled six scoreless innings in St. Louis on Wednesday.

“Little balance to it,” Shildt said. “I like Dylan's at-bats. He's been productive, consistent, and we’ll get him in that five spot. … It [also] puts Carp in a position where he's in there, and he can take a good at-bat and in that post, he’s in as well.”

Monday is the second time this season Carlson has hit in the fifth spot or higher despite hitting cleanup last postseason, and it’s the second time Carpenter has started as low as seventh.