Although the Swiss champions stand a respectable third in a Super League led by Zurich, they are 10 points worse off than this time past year and lost 2-1 at home against Lausanne last Saturday.
"In the Champions League there are four or five teams with an incredible level of quality, of experience, of know-how and that's what makes the difference", he said.
"I don't know", he replied.
Mourinho had said last month before the start of the season that the Sweden global was not yet ready for the Premier League, and said that the player needed time to settle down.
- Tottenham and Dortmund's only previous encounter was in the round of 16 of the 2015-16 Europa League.
Jose Mourinho does not have any fresh injury concerns to deal with ahead of his side's return to the Champions League, with Luke Shaw (foot), Ashley Young, Marcos Rojo and Zlatan Ibrahimovic (all knee) the short-to-long-term absentees. He will play tomorrow but we'll be without him again on Sunday.
The Old Trafford crowd's first encounter with their current manager in March 2004 exposed them to the full force of Mourinho the provocateur.
United has won three of its first four league games and has been more clinical this season, with new striker Romelu Lukaku scoring five goals in five matches in all competitions and midfielders Paul Pogba and Henrikh Mkhitaryan looking more unsafe going forward.
As of now, it is confirmed that the Belgium global will miss his side's first Champions League game in what seems like ages.
United are back in the Champions League after winning the Europa League last season, but Parker believes Lukaku may end up being used sparingly in the competition.
This is Raphael Wicky's first Champions League campaign as manager.
But his stock in the competition has dipped since his second success with Inter Milan in 2010, the Portuguese having failed to go beyond the semifinals in his three years at Madrid and two-and-a-half-year second stint at Chelsea. It's nearly two years without a Champions League game at home. We've worked very hard all of past year in the league and then went through a really tough qualification phase and this is the competition that we wanted to be in. The Swiss side secured a memorable 1-1 draw on their first visit in March 2003 and were on the cusp of a famous triumph in September 2011 after recovering from two early Danny Welbeck efforts to go 3-2 up.
Manchester United have been grouped with FC Basel, Lindelof's former club SL Benfica and CSKA Moscow.