Bruins rookie Phil Kessel left the team's lineup indefinitely Monday for a medical condition "not related to hockey," his family said in a statement released by the team.
But a source familiar with the situation told ESPN.com on Monday that the forward's condition does not involve drugs or alcohol and more information about Kessel's condition will likely be available by the end of the week.
"It has nothing to do with any nefarious activities," the source said.
The family asked that the media and the public respect his privacy.
"At this time there is no further update on Phil's condition," Kessel's family wrote in the statement. "When there is an update, and it is appropriate to do so, we will update everyone on Phil's health."
Boston television station WBZ reported that Kessel was at a city hospital being treated for testicular cancer. Team general manager Peter Chiarelli declined to comment on the report, but the Boston Herald reported that according to a Massachusetts General Hospital spokeswoman, Kessel had been admitted and was in good condition.
Rumors immediately swirled that the fifth overall pick in last summer's entry draft had some sort of substance issues, but the source said that is not the case.
Asked whether Kessel's absence from the team was expected to be long or short term, the source said it could be either, but the answer would likely come by the end of the week. The source added that the family would be more forthcoming with information once that timeframe for treatment and/or recovery was known.
Kessel ended an eight-game points drought with an assist vs. Montreal on Dec. 4 in what has been a disappointing start to his NHL career.
In 27 games, the promising rookie, once expected to be the top pick in his draft class, has registered just nine points and is a minus-8. His pre-draft stock dropped as his production at the University of Minnesota fell, and he acknowledged he was not adequately focused at times during the season.
The 19-year-old played one season at Minnesota before signing a multiyear contract with the Bruins in August. He led Minnesota and was sixth in the WCHA in scoring with 18 goals and 33 assists in 34 games. He also was the career leader in goals for USA Hockey's national development team.
The Associated Press contributed to this report.