Mourinho already lost one Belgian global to injury after Marouane Fellaini was ruled out for two weeks with a knee ligament strain he picked up against Bosnia.
While they have nursed one United star back to fitness, Belgium have seen another laid low while away on worldwide duty.
United are now second in the table, behind neighbours Manchester City on goal difference, and seven points ahead of Liverpool. We are in touch with Man United's medical team.
Martinez said: 'Romelu is fit and available, he's training with us tonight, ' said Martinez.
The club are believed to be concerned that his running style may have been the cause of the injury, and are considering using a running coach in the hope of avoiding a recurrence.
This news means that Jose Mourinho will be without one of his favourite players of recent weeks, as the Belgian has completed 90 minutes in each of United's past three Premier League games.
"But there was nothing wrong in that respect so the relationship is very, very good with Manchester United as you would expect".
The 25-year-old has formed a strong defensive partnership with Eric Bailly this season and Mourinho will be anxious that he makes the weekend trip to Anfield.
Record signing Paul Pogba is a long-term absentee after picking up a hamstring injury against Basel in the Champions League last month and Michael Carrick, who has played just once this season, is also a major doubt for the Liverpool match.