Ten Hag short on strikers for derby as Man Utd wait for Weghorst
Weghorst is set to join until the end of the season after United reportedly agreed a deal with Besiktas to cut short his loan from Championship side Burnley.
Anthony Martial is also a doubt due to injury, which could force Ten Hag into moving the in-form Marcus Rashford into a more central role.
Rashford has scored in eight straight games at Old Trafford and has seven goals in six matches since the World Cup break.
But most of the England international's goals have come when operating off the left rather than through the middle.
"I think we are close," Ten Hag said when asked at his pre-match press conference on Friday about the deal for Weghorst. "But he wouldn't be available for tomorrow."
Weghorst, who scored just twice for Burnley in the Premier League last season, has been seen as an underwhelming replacement for the departed Cristiano Ronaldo by many United fans.
But United have thrived since Ronaldo's contract was terminated, with eight consecutive wins in all competitions.
The acid test will come against defending Premier League champions City, who hammered their local rivals 6-3 when the sides met earlier this season at the Etihad.
"It is not coming overnight, there has been a process in the last months where we develop, progress," said Ten Hag. "We have to be brave, act with belief and play our game.
"We took the lesson (from the last meeting) and from that point on we make huge progress. We have to continue that process."
Diogo Dalot is also missing for United due to an injury picked up in Tuesday's League Cup quarter-final win over Charlton and Donny van de Beek's season is over due to a serious knee injury.
