DAVID Vaughan is set to miss the start of the season after suffering a setback in his recovery from a hernia operation. Vaughan went under the knife during the summer, but broke down in training during Sunderlandâs pre-season trip to South Korea â failing to appear in both encounters in the Peace Cup. The Welsh international is undergoing further treatment on the injury, but is expected to be ruled out for several weeks. And with the Premier League campaign beginning at Arsenal three weeks tomorrow, the 29-year-old is unlikely to be ready for the curtain-raiser at the Emirates. Sunderland boss Martin OâNeill said: âDavid had a hernia operation (during the close season) and didnât feel too bad. âHe had a few injections to sort everything out, did a bit of training on the day after our first game in Korea and felt great, but then the following day he didnât feel so good. âThe medical staff are investigating and they think that they should be able to sort it out. âBut itâs a setback because he could be out for a few weeks again and pre-season is really important.â Vaughan was not the only Sunderland player to suffer an injury in Korea, with goalkeeper Simon Mignolet and defenders Wes Brown and Carlos Cuellar all heading to the treatment room. Mignolet (groin) and Cuellar (thigh) did not suffer serious knocks, although the duo remain doubtful for tonightâs friendly at North East neighbours Hartlepool United. But Brown sustained suspected knee ligament damage during the second Peace Cup encounter against FC Groningen and Sunderland are still awaiting news on the severity of the 32-year-oldâs injury. âWes had a scan on his knee yesterday and we are now waiting for the results,â said OâNeill. âSimonâs not too bad. He had a groin problem but leaving him out of the Groningen game was more of a precaution than anything else and it also gave me a chance to have a look at the two young keepers. âWeâll see whether he recovers in time to play against Hartlepool tonight. Carlos has a thigh injury and itâs not too serious but I donât think he will play tonight.â Meanwhile, defensive duo Matt Kilgallon and Phil Bardsley, who both missed the Korea trip entirely, are making good progress in their recoveries. Kilgallon has resumed full training after picking up a knock during the summer, while the ankle problem Bardsley sustained on the second day of pre-season training is not thought to be as serious as first feared. âMatt has improved sufficiently to do some training with us, which is good,â added OâNeill. âWith Phil, while we were out in Korea he stayed here and made really good progress. It is just a case of giving him a bit longer.â