Lee Nguyen sat out training earlier last week to express his displeasure over the organization’s refusal to renegotiate his contract, a source told New England Soccer Today on Monday.

According to the source, who spoke on the condition of anonymity, Nguyen is “extremely unhappy” with the club’s unwillingness to rework his contract, which is scheduled to pay him a base salary of $175,000 in 2015. The Revolution midfielder is coming off a 2014 campaign in which he scored a career-high 18 goals, added five assists, and was shortlisted for MVP consideration.

Prior to his breakout season, the Revolution midfielder signed a two-year deal worth $175,000 annually with options for a third- and fourth-year, as well as a $40,000 signing bonus in Jan. 2014. The contract was offered to Nguyen with years remaining on his previous deal, which had paid him a base salary of $73,600 in 2013.

The attacking midfielder approached the organization about a new deal during the winter, but the club wasn’t ready to rework a deal that was signed only a year before. Nguyen contemplated sitting out training at an earlier point in the season, but decided against it because of the potential negative impact it would have on his status with the U.S. Men’s National Team.

Ultimately, Nguyen delayed his protest until last week.

After sitting out the earlier part of last week’s training, Nguyen returned to the team because “he didn’t want to disappoint his teammates and fans,” the source said.

But Nguyen wasn’t handed back his spot in the XI upon his return. On Saturday, he was benched in favor of Kelyn Rowe, who went 56 minutes before Nguyen came on and, not long after, assisted on Teal Bunbury’s game-winning goal.

Saturday’s 2-1 win over the Red Bulls marked the first time since the 2012 season opener that a healthy Nguyen did not start for the Revolution.

Following the match, Heaps told the media that Nguyen was not included in the XI after missing training due a “private matter.”

In eight games, Nguyen has struggled to find the form that made him an integral piece of the Revolution’s first run to the MLS Cup final in seven years. To date, he’s only scored one goal – a penalty kick effort at Colorado – and collected two assists.

During the Revolution’s nationally-televised away match at Philadelphia, ESPN broadcaster Taylor Twellman suggested that Nguyen’s disappointing play might be due to the midfielder’s unhappiness with his contract.

Last week, teammate Charlie Davies offered an alternative explanation to Nguyen’s scoring woes.

“I think he’s had a tough start to the season because he came in a little bit injured,” Davies said. “At this point, it’s just his rhythm, it’s getting into a rhythm, and getting sharp. He’s one of those players that you don’t have to worry about his confidence. He’s very confident player, so I think in time, he’ll start to get sharp and find his rhythm.”