PITTSBURGH -- Jordan Walker, MLB’s No. 1 prospect, per MLB Pipeline, officially rejoined the Cardinals on Friday following more than a month of the 6-foot-6, 245 pound slugger reworking his swing at the Triple-A level. To make room on the roster, the club placed outfielder Lars Nootbaar on the 10-day injured list, retroactive to Tuesday, with a lower back contusion.

Walker, who electrified MLB audiences early in the season by hitting safely in the first 12 games of his career as a 20-year-old, was demoted to Triple-A Memphis on April 26, where the Cardinals wanted him to work on an improved launch angle off the bat. In the first 20 games of his MLB career, Walker -- now 21 -- slashed .274/.321/.397 with three doubles, two home runs and 11 RBIs. However, he had a 58.5 percent ground-ball rate, well above the MLB average of 44.8 percent, per Baseball Savant.

In 29 games with the Triple-A Redbirds, Walker hit .239 with four home runs, six doubles and 16 RBIs. He stole four bases without being caught and had half as many walks [16] as he did strikeouts [32]. His fourth home run came on Wednesday night and led to his promotion.

“The timing of [Walker’s hitting improvement] is as you would almost have pictured,” Cardinals manager Oliver Marmol said earlier in the week. “When we were talking about this process [of demoting Walker] we figured that there's going to be a little bit of a period where it didn't look good from a box score standpoint, and then it would start to turn, and he’d get more comfortable and get going. Of late, it looks like he's getting going, which is good. With his at-bats, overall, the reports have been positive.”

Unlike when Walker was with the Cardinals at the beginning of the season, opportunity now abounds in the outfield. Tyler O’Neill [low back strain] and Dylan Carlson [left ankle sprain] have spent extended stretches on the injured list, and Nootbaar had to leave Monday’s loss to the Royals with back spasms. The Cardinals were forced to use Tommy Edman and Brendan Donovan -- both Gold Glove-winning infielders in the past -- to fill in in the outfield during the two-game series against the Royals.

Walker made the Cardinals out of Spring Training despite being one of five outfielders on the roster. Now, he will likely return as a full-time starter in right field and the Cardinals are hopeful that he is at the MLB level to stay.

“None of this is perfect, right? That's cute to think of it that way, but at the end of the day, you’re only in control of certain things and [Walker not being demoted again] is not one of them,” Marmol said earlier in the week. “Sure, [the club doesn’t want to demote Walker again], but three or four years from now, is any of that going to matter? The answer is probably not. So, you want to make sure you're basing it off the probability of what's most likely to happen and make sure that we have a safety net for a worst case. But, yeah, we'd like it to be where he comes up and stays up here.”

Marmol said the Cardinals were always banking on Walker’s advanced maturity, level-headed persona and his high baseball IQ to go to Triple-A and make the changes necessary. Those changes, Marmol said, will not only allow Walker to stick at the MLB level, but they should help him reach his massive potential as an elite power hitter.

“Getting him back here has been the goal the whole time,” Marmol said Monday. “[Walker’s maturity] played a big role; we sent him down because of his maturity.

“There are certain guys that that'll really be a gut punch [for them] going back down there and having to deal with that mentally, and we didn't feel like that'd be an issue for him at all,” Marmol continued. “So, that's what made it a little bit easier to say it is the right move and let's get ahead of it rather than him [struggling] up here and then starting to doubt himself. So, his maturity allowed us to put him down there and we thought he would handle it just fine.”

Walker ranks in MLB’s 93rd percentile in max exit velocity, once hitting a ball 113.9 mph at the MLB level and another at 114.7 mph at the MiLB level this season. In his 20 MLB games, Walker had 25 balls classified as hard-hit [95 mph or harder]. The Cardinals are of the belief that with some improved launch angles, Walker will be driving balls over the wall and into the gaps for more extra-base damage in the future.

"It never crossed our minds that he wouldn't be able to do it,” Marmol said of the hitting adjustments. “I mean, we're talking about a really good hitter and all we want is in order to get the highest level of Jordan Walker, he's got to elevate [the baseball] more. Never did we think he wouldn't be capable of making the adjustment.”