Former Manchester United and Bayern Munich midfielder Owen Hargreaves insist that Chelsea made the big mistake of not signing a proven goalscorer during their spending spree this season.
"Considering they (Chelsea) spent £600m and they don't have a centre-forward is just crazy and that game summed it up," Hargreaves said on pundit duty with BT Sport.
"They need someone who can put the ball into the back of the net," the England ex-international added.
However, Hargreaves believes Chelsea can still qualify despite the 1-0 defeat at Dortmund.
"I think the tie is far from over. I think Chelsea can easily go to the Bridge and win the game in the second leg, but again Dortmund are a threat we saw that."
Echoing Hargreaves's sentiments on Chelsea not signing a striker, Rio Ferdinand said:
"For all the good chances they had and created, and the positives, they'll be in that changing room and they'll be disappointed everywhere.
"You've got to try and extract some positive from it, yeah their approach play was good, but at this level, you have to finish your chances.
"You can't create the number of chances that they did and not finish them and at this level, you get punished if you don't do that and today there were."
Former Chelsea forward Joe Cole slammed Kai Havertz for his low output as Chelsea's main striker.
"There were patches of the game and moments where all the patterns of play; Joao Felix was getting on the ball, Kai Havertz was getting on the turn, and they looked good.
"But it's that final third when you start not scoring goals - I think it's 23 in the Premier League - it's not good enough for where Chelsea want to be," Cole said.
Chelsea were the highest-spending European club this season, spending more money than some leagues combined. The only striker signed by the Blues was David Fofana but the youngster is not proven and certainly not trusted by Potter.
Chelsea have only scored two goals in their last five games.
