Kyle Harrison has long been the Giants' most highly regarded prospect. He's now being called up to the majors for his debut, sources tell FanSided.

The San Francisco Giants are calling up left-handed pitcher Kyle Harrison, the team's No. 1 ranked prospect, sources familiar with the situation tell FanSided.

After the Giants failed to acquire another starting pitcher at the trade deadline, a Harrison call-up was considered imminent. Team president of baseball operations Farhan Zaidi said he was on an "accelerated rehab program" in his return from a hamstring injury, with one source estimating he needed 2-3 starts before making his major-league debut.

San Francisco Giants call up top pitching prospect Kyle Harrison

Harrison, 21, would have debuted already had it not been for the hamstring injury he suffered while doing lunges while working out. But Harrison, regarded as the Giants' best pitching prospect since Madison Bumgarner, will immediately slot into the team's rotation and give the team a glimpse of the 1-2 punch with Logan Webb that they believe has the chance to be dominant.

Harrison is arriving at a time where the Giants desperately need arms. They have been operating with just two traditional starting pitchers – Webb and Alex Cobb – while heavily relying on openers and bulk-inning pitchers.

While Harrison has not pitched deep into games this season – he has thrown over four innings just five times this season – he has recorded 105 strikeouts and flashed elite swing-and-miss stuff. He will need to refine his command in the majors going forward. But in the words of one rival scout, "when he does, he's going to be a household name before too long."

That buzz has been shared by the Giants front office, his teammates in the minors, and even players in the majors. Now, Harrison is only hours away from his long-awaited major-league debut.