(AP) - The Colorado Rockies are about to introduce a top prospect a week after trading the face of the franchise.

Eight days after dealing All-Star shortstop Troy Tulowitzki, top pitching prospect Jon Gray is set to make his major league debut Tuesday night against the Seattle Mariners.

Gray arrived in Denver on Monday after getting word late Sunday that he was being called up from Triple-A Albuquerque.

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"It kind of hit me when I got to the ballpark," Gray said. "It's just now coming into effect what it feels like. It was an awesome high."

The 23-year-old was the third overall pick in the 2013 draft. A hard-throwing right-hander, he was 6-6 with a 4.33 ERA in 21 games - 20 starts - for Albuquerque this season. In his last six outings, he's gone 3-1 with a 2.70 ERA and 38 strikeouts.

The Rockies were being patient with Gray, but his performance over the last month pushed up his timetable - which surprised him.

"I wasn't expecting it, especially on this homestand," he said. "They told me, 'Here is your plane ticket, you're heading out and going to the big team.'"

The Rockies (44-60) dealt Tulowitzki since they're on their way to a fifth straight losing season, and Gray is considered one of the cornerstone pieces of the future.

"I guess it is ironic that the face of the franchise has moved on and we've got one of our young kids that we've been anticipating pitching for us making his debut right after it," manager Walt Weiss said. "We felt like we'd see him at some point this year. And that day has arrived."

Gray has moved quickly through the Rockies' system. He was 4-0 with a 1.93 ERA in nine minor league starts in 2013 and was 10-5 with a 3.91 ERA in 24 starts with Double-A Tulsa in 2014.

He struggled early this season with high pitch counts, which didn't allow him to go deep into games. He had only one start that went beyond the seventh inning, but he's shown steady improvement since late June.

Still, the Rockies weren't ready to bring him up before Tuesday.

"He wasn't going to be up here until everybody felt that he was ready," Weiss said. "That trumped the need of where we are at as a team. We wanted to make sure that he is ready to go out there and he is equipped for a major league game. We feel that he is."

Gray will face Nelson Cruz, who is batting .429 with nine homers and 13 RBIs during a 14-game hitting streak. He's homered in four straight games after hitting his 30th of the season in Monday's 8-7 win over Seattle (49-58).

Cruz is 8 for 14 with three homers and six RBIs in four career games against Colorado.

The Mariners are giving Vidal Nuno (0-0, 2.11 ERA) a spot start after trading J.A. Happ to Pittsburgh before Friday's deadline.

All 21 of Nuno's appearances this season have come out of the bullpen. Over the last two years, the left-hander has gone 3-13 with a 4.08 ERA in 31 career starts with the New York Yankees and Arizona.

Nuno, though, allowed four runs in 13 1-3 innings over two starts against Colorado last year, losing his only decision.

"I think he's certainly capable of giving us five innings," manager Lloyd McClendon told MLB's official website. "He's got a rubber arm, he's started before this year. It's nothing foreign to him. We'll go with him as long as we can go. If he's not in trouble, he'll pitch."