As the Washington Nationals seek to augment a roster core they believe is built for long-term success, an unusual and previously unreported aspect of outfielder Bryce Harper’s contract remains unresolved.

Harper, the No. 1 overall selection in the 2010 draft, reached an oral agreement on his current deal less than a minute before the Aug. 16 midnight deadline to sign picks. The five-year major league contract, rare for a draftee, called for Harper to be paid $9.9 million, including a signing bonus of $6.25 million. However, the Nationals insisted that the contract not contain a clause that would allow Harper to opt out of the contract terms and into baseball’s lucrative salary arbitration system once he was eligible; Harper’s agent, Scott Boras, was equally adamant that the virtually standard opt-out clause be included.

Days later, the Nationals presented a final written contract that did not contain an opt-out clause. Anticipating the possibility that Harper, at the time 17, could reach the majors sooner than expected, Boras and the Harper family refused to sign it.

At that time, Major League Baseball and the Players Association took the unusual step of interceding with a compromise: a letter of agreement stating that, if Harper qualified for salary arbitration before he reached the end of the contract, a grievance hearing would determine whether he could opt of his contract.

Boras and two other people familiar with Harper’s contract confirmed the unusual arrangement. It means that, barring some resolution in the interim, Harper and the Nationals could find themselves on opposite sides of a legal dispute next offseason.

“We reached an agreement with MLB and the MLBPA memorializing that Bryce only signed with the Nationals on the condition that his rights were preserved,” Boras said. “So, as planned when the issue arises, we will proceed under the terms of that agreement.”

Under normal circumstances, players qualify for salary arbitration after accruing three full seasons of major league service time. Among the players with between two and three years in the majors, the top 22 percent in service time are eligible for arbitration early. Following the 2014 season, Harper almost certainly will be among this latter group, known as “Super Two” players.

In the arbitration process, an independent panel, after hearing from both the player and his team, decides on the player’s one-year contract value based on service time, the salaries of comparable players and any special awards. Most players and teams agree to a new salary before a hearing is held. Either way, practically speaking, the process usually means huge raises for players.

In the case of Harper, the 2012 National League rookie of the year and a two-time all-star, his draft deal calls for him to earn $1.5 million in 2015. Presuming he remains healthy and continues to perform at projected levels in 2014, he could land a 2015 salary between $4 million and $7 million through arbitration, were he eligible. Were Harper to get hurt or to decline in performance, he likely would make less.