MINNEAPOLIS –- Willi Castro was just getting out of the clubhouse bathroom during a blowout loss for the Toledo Mud Hens Friday night in Columbus when he was told to sit down. He wondered if he was being disciplined for something. Instead, Hens manager Doug Mientkiewicz was giving him the news many Tigers fans have been anticipating for weeks.

“He told me that I got called up, and it was an emotional moment,” Castro said, “something that I wasn't expecting.”

With that, the Tigers’ shortstop of the future joined them in the present, called up Saturday for his Major League debut. He was in the Tigers' lineup on Saturday night, batting seventh and starting at shortstop.

Expect to see his name in the lineup a lot down the stretch. What was expected to be a late-season audition with September callups was moved up a week by Niko Goodrum’s trip to the injured list with a left groin strain.

“We had talked about bringing him up anyway,” manager Ron Gardenhire said. “But when it's all said and done, you start thinking about the ramifications of bringing him up, and it's probably to release somebody. Another week would've been fine, but with an injury, it's easy just to put [Goodrum] on the IL and bring him in.”

Castro, the club's No. 11 prospect according to MLB Pipeline, is the second critical position player of the Tigers’ rebuilding project to be called up in the past four weeks, joining catcher Jake Rogers. The 22-year-old Castro, acquired from Cleveland in the Leonys Martin trade last July, had been knocking on Detroit’s door for much of the summer with a standout season at Triple-A.

The switch-hitting Castro batted .301 (140-for-465) in 119 games with the Mud Hens with 28 doubles, eight triples, 11 home runs, 62 RBIs and an .833 OPS. His .383 average (31-for-81) in August, including five home runs and 17 RBIs in 20 games, increased the sense of inevitability.

“I've just tried to focus on good pitches,” Castro said. “Sometimes I get too quick and attack the ball too much, and that's when the strikeouts come. I just try to be patient, and it's something that has been helping me a lot this year.”

While 22 errors in 111 games at short marked an increase from last year, creating speculation about Castro's positional future, he has worked with Hall of Famer and Tigers special assistant Alan Trammell on improving his throws, the main source of his defensive miscues.

“This year, I think my hitting has improved a lot. I know I can get better on my defense, too,” Castro said. “I've been feeling way better now than when I started with my defense, a couple errors that I made early in the year.”

Castro will get plenty of opportunities to show his long-term fit. The Tigers are calling him up with the expectation to play him regularly. While he could help fill Goodrum’s void at second, having started 16 games there over the past couple of years, the big question the Tigers want to answer is whether Castro is ready to take over at shortstop next year.

Castro arrives at the same time Jordy Mercer is enjoying his best offensive stretch of the season, batting .339 (20-for-59) and an .852 OPS in August. But Mercer knew since Spring Training that Castro would eventually be called up and shift his role, a matter Gardenhire discussed with him earlier this month.

“I knew this day was coming,” Mercer said. “We talked about it for a few weeks and we've been putting a plan together. I'm going to start bouncing around and play other positions and show teams I can play other positions, show this team I can play other positions."

Said Gardenhire: “I always go to the veterans. I want them to know what's going on. I don't want them to be surprised. Sometimes it's not good, because they don't react very well to it. But still, I've always been a person to tell them exactly what's going on if I can.”

Quick hits

• Goodrum is scheduled to get an MRI exam in the next couple days to determine the extent of his groin injury and figure out if he has a realistic chance to return this season.

• Catcher Grayson Greiner, who was on a rehab assignment with Triple-A Toledo for the past week, was reinstated from the injured list and optioned to Toledo. Greiner went on the IL on June 15 with a low back strain. He’s expected to rejoin the Tigers once rosters expand in September.