According to ESPN.com's Brett Okamoto, Ferguson posted the following message after he underwent elbow surgery, which isn't expected to keep him out for an extended period of time: "I asked Doc if he could make my elbows any more sharper. Well ... [with] a wink and a nod it was done!!! T'was a very minor surgery and now getting ready to unify my belt with McNuggets in the first [quarter] of the year (March - April), as recovery is going great!!! #DefendorVacate."
The 33-year-old Ferguson became interim champ at UFC 216 in October when he defeated Kevin Lee by submission.
McGregor won the lightweight title at UFC 205 in November 2016 when he knocked out Eddie Alvarez in the second round.
The Irishman hasn't fought for the UFC since then, though, as he shifted his focus to boxing. McGregor went on to lose to Floyd Mayweather Jr. by 10th-round technical knockout in August.
There is significantly more money in boxing than mixed martial arts for McGregor, and this week, boxing legend Manny Pacquiao said he reached out to McGregor about a potential fight, according to Okamoto.
In the MMA world, McGregor is the sport's biggest draw, and he is among its most successful competitors with a record of 21-3.
Ferguson is 23-3 and is in the midst of an impressive 10-fight winning streak.