Bolton will be without defender Ricardo Gardner until October while he recovers from a third cruciate knee ligament operation.
The 27-year-old Jamaica captain has been sidelined since the penultimate game of last season and was under the supervision of top specialist Dr Richard Steadman in the United States before continuing his rehabilitation at the team's training camp in Switzerland.
Steadman aided Gardner's recovery from similar injuries in 2000 and 2004 and manager Sam Allardyce is optimistic of a positive outcome on this occasion.
He told the club's official website: 'Ricardo had a successful operation and as things stand he should be back in action during October.
'He is currently going through an intense rehabilitation programme with the sports science team in Bad Ragaz.
'It is a blow to our preparations for the start of the new campaign, but Ricardo is a strong character and will return in a positive manner.'
Meanwhile, new signing Idan Tal - who joined up with his new team-mates in Switzerland this week - cannot wait to get started at Wanderers.
The 31-year-old former Everton midfielder, who has completed the formalities of his move from Israeli champions Maccabi Haifa, said: 'This is a fantastic club and the spirit in the camp is in evidence.
'Training has been very intense, but enjoyable. The coaching staff do expect you to give every bit of energy to the camp.
'We have trained every day for around six hours and there has been a diverse range of activity, from cycling up mountains to intense cold therapy in a large freezer cabin.
'Bolton prides itself on being a very forward-thinking club with innovative methods.
'The training schedule has been totally different to what I have experienced at other clubs. Bolton has a major emphasis on preparation and fitness and this is why the club are very successful.'
The Israel international added: 'Bolton have made rapid strides in the last few years and I have taken note of their efforts in the Premier League.
'The potential at Bolton is massive. I want to play a major part in making the club's ambitions come true.'
Tal feels he can realise his potential under Allardyce.
'Sam Allardyce has impressed me during negotiations,' Tal said. 'His humility was one of the main reasons why I wanted to sign for the club.
'He makes you feel special and certainly knows how to get the best out of you.'