Chelsea have put in an official offer for the Roma defender Walter Samuel, considered to be one of the world's best centre-backs. The hard-up Italian club, who lost out on the Serie A title when they were defeated at Milan on Sunday, are looking for £17 million, though Chelsea's Roman Abramovich wants to reach agreement at £15 million.

According to sources close to Roma, the London club will offer a four-year contract worth £2.7 million a season to the Argentinian international nicknamed "The Wall" by fans at the Stadio Olimpico.

Samuel's agent, Raul Oliveros, and adviser, Abel Balbo, have refused to confirm the details but admitted that negotiations were under way. "Chelsea made a big offer that Roma are considering," said Balbo.

Oliveros added: "Chelsea's offer is huge and will be impossible for both the player and Roma to refuse."

Samuel (26), is seen by Chelsea as a perfect long-term replacement for Marcel Desailly, who will turn 36 in September. The Argentinian, who is under contract with Roma until 2006, is keen on moving to Stamford Bridge where he will be united with his countrymen Juan Sebastian Veron and Hernan Crespo.

"I'm attracted by the idea of playing in England," he said last week. Samuel moved to Roma from Boca Juniors for £13 million in 2000.

Roma have said they will need to sell players to offset debts of £162 million. They are still paying players' salaries from last year.

The club's sporting director, Franco Baldini, has confirmed Chelsea's interest in Samuel but also refused to unveil financial details of the offer. "We have been in contact with Chelsea and they want to sign Samuel. However, the contacts we had were just informal as we still have two league matches to play. It's not time to speak about the transfer market yet," he said yesterday.

Commenting on Roma's financial situation, Baldini admitted: "Maybe we will have to sell some important players, but if this happens, we will sign other players who are as good as those leaving. We want to be competitive next season."

Meanwhile, Frank Lampard has revealed how Chelsea's frustration at the way they lost to Monaco in the first leg of their Champions League semi-final has turned into determination to make it through to the final.

The in-form Blues midfielder also praised coach Claudio Ranieri for admitting he got it wrong in Monaco with his bizarre substitutions, as the team lost 3-1 against 10 men.

Chelsea were in control and looking good for a vital away win when the score was 1-1 and Monaco had a man sent off, but two late goals left the Londoners with a mountain to climb at Stamford Bridge in the return tomorrow night. At first the players were shell-shocked and Ranieri was heavily criticised for his tactics.

But Lampard said the players must share the blame, and they believe they can turn around the tie.

"Of course all the players were frustrated by the way the game went," said Lampard. We dominated almost until half-time and felt confident, then we lost it 3-1 to 10 men, so it is understandable that people make a big deal out of it.

"But in time you calm down and the frustration turns into a determination to put it right. The way the game went it was obviously a bad result, but if you put it into context, 3-1 away was not a terrible result Champions League-wise. We'll have to set our stall out to be strong and believe we'll take our chances, because we know we'll create them.

"We have to believe we can still make it. We scored four goals against Southampton on Saturday and that will help us because we have confidence now. We have to make sure we don't try all-out attack, we have to be clever and hopefully we'll win the game.

"We showed great determination and character to beat Arsenal in this competition and we were very focused in the build-up to it. If we can show that same focus we can go out and perform the way we did at Highbury.

"We need patience, belief and to take our chances. We have been strong at the back and if we can get a goal in the first half we can go on and win."

Lampard described the depth of the mood around the club after the defeat and said everyone was to blame, not just Ranieri.

He added: "The evening after the game was very hard for the players and we were all talking about it through the night, and the next couple of days were hard because of the nature of the game. We are desperate to get to the final and we felt we had a great chance to put them out of sight but we didn't do it.

"We didn't blame the manager, a lot of that came from outside. To give the manager credit, he came out and said he made a mistake, but the players also made a mistake because in the second half we were not the same team. The substitutions were made but we still had good players in every position. We have to take a lot of the blame."