United had scouts watching Waris during Trabzonspor’s 2-0 win against Lokeren in the Europa League on Thursday 23 October.
Waris was closely linked with Ligue 1 side Lille and Premier League outfit Leicester City last summer however, both clubs were unable to agree upon a fee with his parent club Spartak Moscow.
The highly rated Ghanian international was named the Swedish top flight’s best player in 2012, after finishing as the league’s top scorer with 23 goals in 29 games for Hacken.
Waris joined Spartak Moscow in 2013 and spent last season on loan at Valenciennes where he found the back of the net 10 times and made five assists in 21 appearances.
The 22-year-old joined Trabzonspor for €6 million this summer and has one assist in six appearances this season.
Waris was part of the Ghanian national team which competed at the World Cup in Brazil this summer.