John Clayton explains the details surrounding Todd Bowles' hospital visit and his desire to coach the Jets on Saturday against the Patriots. (0:45)

New York Jets coach Todd Bowles was admitted to a hospital Friday afternoon with an undisclosed illness and didn't travel with the team for its road game Saturday against the Patriots, the Jets announced.

Bowles, 53, is in stable condition, according to the team. Sources told ESPN NFL Insider Adam Schefter that while the team initially feared Bowles had a heart attack, doctors have determined that was not the case.

The Jets said his availability for the game is uncertain. If he can't make it to Foxborough, Massachusetts, for the 1 p.m. kickoff, the head-coaching duties will be handled by assistant head coach Mike Caldwell.

Caldwell ran the walk-through practice Friday at the team facility. Jets general manager Mike Maccagnan has visited Bowles in the hospital and, upon his arrival in New England, updated the team of the coach's health status.

Todd Bowles has been hospitalized and did not travel with the team to New England. Brad Penner/USA TODAY Sports

"I knew [Bowles] hadn't been feeling great [Friday morning]," a source told ESPN's Josina Anderson. "He said he felt tired."

The source noted that Bowles didn't seem sick at the time of the interaction.

This has been a difficult season for the second-year coach, who has come under fire because of the Jets' 4-10 record.

Bowles led the Jets to a surprising 10-6 mark in 2015, raising expectations for this season, but the team has endured two four-game losing streaks.

The Jets were blown out at home Saturday night, losing to the Dolphins 34-13.

There has been speculation about Bowles' job security, but owner Woody Johnson is thought to be leaning toward retaining Bowles, who has a four-year contract.

This is the second time this calendar year Bowles has had a medical issue, as he had a benign mass removed from his throat in February. Sources told Schefter that doctors want to visit with Bowles again after the season and continue to monitor his health.

Bowles is the third NFL head coach to suffer an in-season medical emergency. Broncos head coach Gary Kubiak experienced a complex migraine condition that forced him to miss one game, and Vikings head coach Mike Zimmer missed one game to undergo emergency eye surgeries.

Information from ESPN's Josina Anderson and The Associated Press contributed to this report.