Chelsea are favourites to land Spurs midfielder Modric.
The Mirror says confirmation of the move for Marin suggests the north Londoners are looking at replacements for Modric.
Marin, who cost Bremen £7.5m from Borussia Moenchengladbach in 2009, has two years left on his current deal.
Although his club have rejected Tottenham's initial interest, Marin has admitted he would be willing to leave Bremen should they receive and offer they cannot refuse.
"If the club receives an offer and decides to sell me, that is another situation," he said. "Until then, I am happy here.
"I want to stay at Werder. I feel good at Bremen. I have never had the urge to leave. I want to be successful here, and that is my only aim."