Mauricio Pochettino said Friday that Chelsea could have to go back into the transfer market after Blues forward Christopher Nkunku underwent knee surgery.
The 25-year-old French international joined London club Chelsea in June from RB Leipzig for a reported £63 million ($80 million). But earlier this week the club said he would be out of action for an "extended period".
Nkunku, who missed last year's World Cup finals due to a left knee problem, suffered the injury during a pre-season friendly against Borussia Dortmund in Chicago last week.
Chelsea managed a mere 38 goals last season, with Nkunku and fellow new signing Nicolas Jackson brought to Stamford Bridge in a bid to revive Chelsea's fortunes up front under the leadership of former Tottenham manager Pochettino.
With Romelu Lukaku keen to return to Italy, where he had a loan spell with Inter Milan last season, Armando Broja recovering from injury and Pierre-Emerick Aubameyang having left the club, Jackson is Chelsea's only recognised striker now available for their Premier League opener against Liverpool on Sunday.
"We feel sorry about (Nkunku) because he was doing well," Pochettino told a news conference on Friday. "He was an important player for us, his quality is there, one of the best offensive players, can play in different positions.
"It's a big issue for us. But now it's about not thinking too much about the injuries, and being positive.
"We're working on the market also because we're going to miss one player like this, offensive. The club is working to try to find a solution, maybe short-term, maybe long-term, to add the right profile."
Pochettino, meanwhile, refused to comment on Chelsea's interest in Moises Cacedo.
Liverpool manager Jurgen Klopp confirmed on Friday the Reds have reached an agreement with Brighton for the transfer of Caicedo, for a reported British record fee of £110 million ($140 million, 127 million euros).
However, Sky Sports reported the 21-year-old Ecuador midfielder is still to decide his future with Chelsea also interested.
Both Chelsea and Liverpool are looking to rebuild their squads after disappointing campaigns last season, but Pochettino said he faced a tougher task than Klopp.
"I think we are more in transition than Liverpool," he said. "Because I am new here, and Klopp is for seven years at Liverpool. In seven years you can anticipate the transition, you can see what is going to come, you can be ahead of the problems.
Pochettino, however, added: "Of course, we are Chelsea, the history of the club is to win, even if we are in transition, people know we cannot give the message that we are in transition. We need to win and we need to be ready to win. And we are going to be ready to win against Liverpool.
"The mentality for the players and the whole club is about how to compete in the best way to be strong and to really believe in us. I'm not going to accept a different way to think.
"Excuse? OK, for other people, but no excuse for us, because we need to be strong."
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