Chelsea, who were beaten 1-0 by Borussia Dortmund in the Champions League on Wednesday, spent more than $350 million to bring in eight players in January but did not sign a proven striker.

With Pierre-Emerick Aubameyang left out of their Champions League squad, on-loan forward Joao Felix hit the woodwork as Chelsea registered 21 shots against Dortmund, including eight on target, in the first leg of their last-16 tie.

The return leg will be played on March 7 in London.

"We have had a lot of new players join in this window and I think you can definitely see us improving and getting that chemistry with one another now," Havertz said.

"This was another step forward, even though we lost. The result...wasn't what we wanted, but I think we showed some good signs – especially in the second half – and we need to build on that."

Since manager Graham Potter took over in September Chelsea have scored only 25 goals in 24 games and managed only three in their last eight.

Last month's 1-0 Premier League win over Crystal Palace remains their only victory in nine games this year.

Against Dortmund, Felix also hit the crossbar while Kalidou Koulibaly and Enzo Fernandez, who joined Chelsea for a British record fee of more than $130 million, were denied by goalkeeper Gregor Kobel.

"I don't think we should be too unhappy with our performance because we created the opportunities, but it's just frustrating that we couldn't take any of them," Havertz said. "We have to look at that and try to improve on that front."