After jumping to second place in the tracking poll with 15 percent support at the end of last week, Rubio has dropped by 2 percentage points since Friday, earning 13 percent support in the Monday poll.
The Florida senator tied for second place with Sen. Ted Cruz (R-TX), who dropped one point since Friday in the UMass tracking poll.
Former Florida Gov. Jeb Bush and Ohio Gov. John Kasich both earned 10 percent support in the poll released on Monday.
According to TPM's Polltracker Average, Trump leads in New Hampshire with 31.2 percent, followed by Rubio with 16.7, Cruz with 12.4, and Kasich with 12.4.
UMass conducted the poll for Boston news station WHDH. UMass surveyed 464 likely Republican primary voters Feb. 5-7 via phone with a margin of error plus or minus 5.13 percentage points.