Manchester United are monitoring the performance levels of Borussia Dortmund midfielder Axel Witsel and are considering a potential move for the Belgian as part of their plans to strengthen the squad in January.

United manager José Mourinho was spotted in the stands during Belgium's Nations League victory over Iceland last week and according to HLN, via the Metro, the Portuguese was in attendance to watch Witsel in action.

It is believed that the Red Devils were interested in the 29-year-old in the summer already, before he ended up moving to the Bundesliga from the Chinese Super League, but given the current state of matters at United, Mourinho is in serious need of some fresh blood to get the team to a good finish in May.

And Witsel could be just the man to give United the needed spark with the club struggling to get the best out of Nemanja Matic in the midfield. The former Chelsea man was slated for his poor defending that led to Ilkay Gundogan scoring Manchester City's third goal in their derby win over United last weekend.

Matic, in general, has been struggling this season to produce similar performances that led Chelsea to the Premier League title in 2017 and could soon fall out of favour with Mourinho.

The addition of Witsel will, however, be a complicated one if United want to secure him in the upcoming transfer market. Witsel has been on hand in Dortmund's incredible season so far, starting in all but one of their league matches, while he's played the full 90 minutes in all four of their Champions League encounters.

Dortmund are currently top of the Bundesliga and are in a good position to win their first league title in six years, which will make it quite difficult for United to pin him down halfway through the season.

But given United's desperation to improve their team, a massive bid could maybe get the German outfit to consider selling.