Nolan Arenado is that rarest of rookies — one who might make an Opening Day roster without regard to service-time considerations.

The Colorado Rockies likely will wait another 7-10 days before deciding whether Arenado will be their starting third baseman. But the team is giving the idea serious consideration, according to major-league sources

“It’s a tough call,” one club official said.

Chris Nelson, the team’s incumbent third baseman, batted .344 with an .881 OPS in 180 at-bats after the All-Star Game. But Nelson, 27, lacks an established track record, and the Rockies might simply decide it is Arenado’s time.

For Arenado and surging rookies such as Boston outfielder Jackie Bradley Jr. and Minnesota outfielder Aaron Hicks, the final weeks of spring training will be critical as they face pitchers sharpening their repertoires in advance of Opening Day.

Teams generally hold off on promoting rookies immediately in order to delay their eligibility for salary arbitration and free agency. But the Rockies are willing to make an exception for Arenado, who is batting .276 with a 1.069 OPS in 29 at-bats this spring.

Arenado is a gifted defender, and should fit well in an offense that the Rockies expect to be quite productive. Nelson probably isn’t strong enough defensively at second and short to be an effective utility man, and he is out of options, which could lead to a trade.

The Rockies want to add one more veteran starting pitcher, and Nelson isn’t their only potentially expendable part. The team wants to move catcher Ramon Hernandez, and will assume part of his $3.2 million salary to make a deal, sources say.

Hernandez, who turns 37 on May 20, is expendable because the Rockies are likely to name Yorvit Torrealba the backup to Wilin Rosario, with infielder/catcher Jordan Pacheco giving the team another option.