The fee has been agreed for the former Celtic, Morton and Newcastle man, but personal terms were being discussed late last night.
Special arrangements were being made to complete his medical before the match. "With the kind of money invested in this day and age I think it is vitally important players are found to be physically fit, and we wanted Alex to complete both parts of a medical," manager Paul Sturrock said.
In spite of the efforts though, the most likely scenario is that the player will join United on Monday. Sturrock remains confident once formalities are complete, Mathie, 29, will strike up a profitable partnership with Scotland forward Billy Dodds.
The Tannadice outfit were disappointed to lose Gary McSwegan to Hearts last week, but Sturrock feels Mathie will prove the ideal replacement.
He said: "Gary had started to form a good relationship with Billy, so when he left for Hearts, I recognised it was important to find something similar. I believe Alex can develop the same understanding with Billy as they are both fine goalscorers and have the ability to work for each other."
Canadian international defender Jason de Vos, captured for pounds 400,000 from Darlington earlier this week, is expected to make his debut against the high-flying Rugby Park outfit.
Elsewhere, Aberdeen manager Alex Miller confirmed Jim Leighton will play for the Dons at home to Dundee today - but yesterday refused to talk about the veteran goalkeeper who announced his surprise international retirement this week.
Miller preferred to focus on the opposition at Pittodrie, admitting they will be a tougher proposition to that defeated 2-0 at Dens Park on the opening day of the season.
He said: "We are looking forward to an improvement in terms of the kind of team performance we have offered latterly and we know it is vital we create more chances.
"But it won't be easy against Dundee who have made strides since that season opener."
Dundee boss Jocky Scott agreed: "We were a bit naive when we first hit the Premier League, but we have come to terms with the level of play required, so we must be positive."
Billy Davies takes charge of Motherwell for the first time at St Johnstone promising a clean slate at Fir Park after the ill-fated Harri Kampman regime.
He said: "It is important everyone realises they are starting again and they will be judged along those lines. The most vital aspect, however, is that they realise they have to get back on the winning trail."Reuse content