Manchester United continued their struggle under Jose Mourinho on Saturday when they played out a home draw with Crystal Palace.
The Red Devils failed to assert themselves on the match, leaving many questions to be asked of their midfielder set up.
On this back of this performance, Mourinho has reignited his interest in Borussia Dortmund midfielder, Axel Witsel, with sources the Portuguese's trip to Belgium during the international break centred around scouting the 29-year-old.
Mourinho told reporters on Friday that he had travelled to Brussels for the UEFA Nations League clash with Iceland in order to monitor Romelu Lukaku's fitness following a hamstring injury.
But, although Lukaku was ruled out of the game before travelling to Antwerp for further treatment, Mourinho remained in Belgian capital to watch Witsel win his 100th cap in the 2 - 0 victory for Roberto Martinez's team.
Mourinho has been a long-term admirer of Witsel and had been keen to sign the former Benfica and Zenit St Petersburg player last summer.
United instead spent £52 million to sign Fred from Shakhtar Donetsk, with the Brazilian midfielder's age -- 25 -- a key factor in him being preferred ahead of Witsel, who completed an £18m move to Dortmund from Chinese Super League outfit Tianjin Quanjian after helping the Belgians to third place at the World Cup.
Witsel has made an impressive start to life in Germany with Dortmund, helping the club to the top of Bundesliga -- nine points clear of fifth-placed Bayern Munich -- at the same time as being a key figure in their Champions League campaign.
Mourinho is determined to improve his midfield options at Old Trafford and he believes that Witsel possesses the quality and experience to make a significant difference to his team. United have no plans to make a move for Witsel in January, with Mourinho instead planning for summer reinforcements.
Paul Pogba's long-term future at Old Trafford remains uncertain, while Nemanja Matic's loss of form this season has also raised questions over the Serbia international's prospects at United.
Mourinho will, however, have to convince United that a move for Witsel would make financial sense with the player due to turn 30 in January.
But while Dortmund would be resistant to selling Witsel after just one season at the club, a significant fee for the player next summer could persuade the Bundesliga leaders to sell.