NFL Network's Ian Rapoport provided details:
The injury is "nothing to be worried about" and isn't expected to keep Gronk out of Sunday night's game against the Detroit Lions.
After going off for seven receptions, 123 yards and a touchdown in New England's Week 1 win over the Houston Texans, Gronkowski struggled last week.
The supremely talented Jacksonville Jaguars defense limited the All-Pro tight end to just two grabs for 15 yards in a 31-20 loss.
With wide receiver Julian Edelman suspended for two more games, Gronk is quarterback Tom Brady's unquestioned top weapon in the passing game.
If his ankle injury is worse than expected, Brady will be forced to lean on an unheralded receiving corps led by Chris Hogan.
New England also acquired wide receiver Josh Gordon from the Cleveland Browns for a fifth-round pick earlier this week, and he could potentially be a factor on Sunday night.
In terms of tight ends, former Indianapolis Colts standout Dwayne Allen and Jacob Hollister are the backup options behind Gronkowski.
Assuming Gronk is good to go, he will have a chance to feast on a Lions defense that is tied for last in the NFL with 39 points allowed per game.