Between the impending promotion of Keegan Thompson and optimism surrounding key injured players, the Cubs roster is nearing a boost of reinforcements.

Thompson will take the ball Saturday against the Royals at Wrigley Field as he officially moves into the Cubs’ starting rotation.

The rookie right-hander made 27 appearances (1 start) with the big-league club earlier this season and was sent down to Triple-A Iowa in late July to get stretched out as a starter.

He was 3-2 with a 2.21 ERA and 1.28 WHIP in those 40.2 MLB innings and he’s carried that success into the minors. In 4 starts with Triple-A Iowa, Thompson did not give up a run and permitted only 5 hits while striking out 16 in 14.2 innings.

He tossed 4.1 perfect frames his last time out (last Sunday) and built up to 61 pitches.

“Really good stuff – threw strikes, some strikeouts in there,” David Ross said. “Efficient with his pitch mix, just a normal start where he dominated. You have these guys go down there and dominate, which they should with the success he’s had here.

“[It’s just about] getting his pitch count up. It’s a good indication that as soon as they’re ready to be able to start and give you some length, then they’re ready.”

Thompson joins Justin Steele in the rotation as the Cubs get a glimpse at what these young pitchers can do as starters over the final few weeks of the season.

Thompson and Steele gave the team’s pitching staff a jolt early this spring and when Steele went down with a hamstring injury in late May, the Cubs opted to stretch him out as a starter during his rehab. The 26-year-old southpaw has a pair of starts in the big-league rotation so far, including a 4-inning outing this week in Cincinnati.

“We’re looking forward to seeing how much success these guys can have in the starting rotation,” Ross said. “They’ve already done a nice job out of the bullpen.”

Meanwhile, a quartet of players continue to progress well from injury.

Adbert Alzolay (hamstring) threw a bullpen Friday at Wrigley Field and Nico Hoerner (oblique) went through a full pregame routine, including batting practice and taking groundballs at shortstop.

Willson Contreras (knee) had a checkup with the doctor Friday and hit in the batting cage.

Dillon Maples (blister) also continues to rehab with Triple-A Iowa and threw 2 innings Wednesday.

The plan for Hoerner is to work in Chicago throughout the weekend and the Cubs hope he can head out on a rehab assignment early next week. He has been out since July 28 with an oblique injury.

The team will see how Alzolay responds Saturday after the bullpen and assess from there. He left his start Aug. 13 with hamstring tightness and landed on the 10-day IL the following day.