The Ghanaian, 27, spent last season on loan at Sunderland but the Black Cats turned down the opportunity to secure the midfielder on a permanent basis.
His Inter contract expires in the summer, however, and he has reportedly agreed personal terms with rivals AC Milan.
The news has infuriated Inter, who are understood to have told the midfielder to find a new club for the second half of the season.
New R's boss Mark Hughes is said to be aware that he cannot sign the former Udinese player on a permanent contract, but would welcome his addition until the end of the season.
Muntari has played 66 times for his country, scoring 18 goals in the process.