London - Maurizio Sarri said Chelsea have no chance of competing with Manchester City and Liverpool next season unless their two-window transfer ban is overturned.
Chelsea were hit with the ban for breaches of the international transfer rules on minors and FIFA threw out their appeal against the decision on Wednesday.
The Blues will take their fight against the transfer embargo to the Court of Arbitration for Sport (CAS), but it was the worst possible news for Sarri ahead of Thursday's Europa League semi-final second leg against Eintracht Frankfurt.
Having booked a place in next season's Champions League after securing a top four finish in the Premier League, Chelsea are bidding to win the first trophy of Sarri's reign in the Europa League.
They are favoured to reach the final after drawing 1-1 in Frankfurt in the first leg last week.
But Sarri is concerned that a potentially uplifting end to hs troubled first season would be erased if Chelsea are unable to sign the players he believes are needed to fight City and Liverpool in the Premier League.
"It's very difficult to cover the gap at the moment; we need to work, probably we need to do something from the market," said Sarri, whose third-placed team are 24 points behind leaders City.
"So it's not easy, because the level of the top two is very, very high. As we can see in Europe, so it's not easy.
"Of course, we have to work and we have to try. In my opinion we can reduce the gap.
"I think that we have to buy only one, two players, otherwise it's very difficult to improve immediately.
"I think we are a very good team, so we need only one, two players, no more."
FIFA confirmed it has "partially upheld" Chelsea's appeal, but only in allowing the club to sign European players aged under 16.
The ban on signing over-16s remains in place, leaving Chelsea unable to make changes to Sarri's squad unless they win the CAS appeal.
With Real Madrid expected to make a move for Blues star Eden Hazard, who is out of contract next year, Sarri could be forced to sell a player he would prefer to keep rather than risk losing him for nothing when his deal expires.
That would further weaken his options, but the Italian remains intent on staying with Chelsea next term.
The former Napoli manager insists he would be able to survive without new signings at Chelsea next season, despite the obvious impact on his team's development.
Asked if he would be ready to promote youth talents to the senior squad, Sarri said: "I like to play with young players, so for me it's not a big problem.
"At the moment, we spoke one month ago about the pre-season, the program of the next season.
"But we didn't speak about the market, also because at the moment we don't know if we'll be able to go into the market."
Meanwhile, Eintracht manager Adi Huetter revealed Liverpool boss Jurgen Klopp has sent the Bundesliga club a good luck message.
Klopp urged underdogs Eintracht to follow Liverpool's example after the Reds' stunning Champions League semi-final comeback against Barcelona on Tuesday.
Liverpool overturned a 3-0 first leg deficit with a 4-0 win and, while Eintracht don't have to author such a dramatic escape, Huetter was happy to get the greeting from Klopp.
"He wished everything for Eintracht Frankfurt, and I did congratulate him for reaching the final," Huetter said.
"If you really believe in something it shows you can put that across to your team.
"His team played the way they had all year, and I hope that's what my team can do.
"Everything is possible. The favourite is Chelsea but once you get this far you want to get into the final."