The volatile Senegal striker was left frustrated after failing to make the starting line-up in the opening day defeat by Newcastle.

He stated that he would be seeking talks with the manager and the chairman Phil Gartside.

Lee said: "Diouf is always talking to me and I am pleased he is disappointed.

"We felt it was the right starting line-up. Unfortunately Ricardo Vaz Te was injured and had to come off.

"Everyone then saw Diouf's quality and I can understand his frustration.

"But I want competition for places. I do not want people to feel they are automatic choices.

"It is important people are always looking over their shoulders and being spurred on by other players."

Diouf could return to the side on Wednesday against Fulham at Craven Cottage as Kevin Davies (hamstring) and Vaz Te (foot) are both ruled out.

O'Brien could make his debut after signing a two-year deal with the option of another 12 months following his move from Portsmouth for an undisclosed fee.

The versatile 29-year-old Republic of Ireland international, who played for Newcastle and Bradford before joining Pompey in 2005, becomes Lee's 12th summer signing.

Lee said: "He is a nice one to have on board. One thing Andy brings is Premier League experience.

"I have been impressed with his defensive qualities throughout the years and he is good addition to the squad."

Davies could be sidelined for up to six weeks after tearing a hamstring while Vaz Te is having a scan later today on a foot injury.

Davies has been a big player for Bolton and Lee is disappointed the striker has picked up an injury at the start of the season.

Lee said: "It is obviously a massive blow as he is such an influential player but it gives someone else the opportunity to stake a claim."

Meanwhile summer signings Christian Wilhelmsson and Daniel Braatan will both have a run-out for the reserves against Manchester City tonight.