TSN reported the offer and said Thomas could decide on it by Wednesday.
Thomas' agent, Markus Lehto, told TSN his client wants to be a starting goalie, not a backup.
Shortly after the Bruins were eliminated from the 2012 Stanley Cup Playoffs, Thomas, 39, announced on his personal Facebook page he would not play in 2012-13 despite having one year left on a four-year, $20 million contract. He wrote that he needed to reconnect with his friends, family and faith.
Thomas was suspended by the Bruins for failing to report for the 2012-13 season and was traded Feb. 7 to the New York Islanders, who used his contract to stay above the NHL salary-cap floor.
Earlier in the offseason, Thomas announced through his former agent, Bill Zito, that he would be attempting a comeback for the 2013-14 season. Zito, now the assistant general manager for the Columbus Blue Jackets, no longer represents Thomas.
Thomas led the Bruins to the Stanley Cup championship in 2011 with a 1.98 goals-against average and .940 save percentage in the playoffs. He won the Conn Smythe Trophy and would later collect his second Vezina Trophy for going 35-11-9 with a 2.00 GAA and .938 save percentage in the 2010-11 regular season.
He created a stir Jan. 23, 2012, when he chose to not join his teammates at the White House, where they were being honored by President Obama for winning the Stanley Cup. Thomas used his personal Facebook page to voice the reason he was not in attendance, writing, "I believe the Federal government has grown out of control, threatening the Rights, Liberties, and Property of the People."
Thomas won the Vezina Trophy in 2009 after going 36-11-7 with a 2.10 GAA and .933 save percentage. He was the Bruins' No. 1 goalie from the middle of the 2005-06 season until he decided to take a year off from hockey.
Thomas has played 378 games in the NHL, all with the Bruins; he has a 196-121-45 record with a 2.48 GAA, .921 save percentage and 31 shutouts. Thomas represented the United States and won the silver medal as Ryan Miller's backup at the 2010 Vancouver Olympics.
Markstrom, 23, the Panthers' second-round pick (No. 31) at the 2008 NHL Draft, is set to become Florida's starting goaltender after the team declined to re-sign veteran Jose Theodore. Michael Houser, an undrafted 20-year-old who spent last season with the Cincinnati Cyclones in the ECHL, would be next on the depth chart.