* Bieber has verbal altercation with photographer
* Still feeling "under the weather" after hospital stay
* Latest setback in "rough week" for Canadian star
* To return to stage after collapse (Adds verbal altercation, background)
LONDON, March 8 (Reuters) - Canadian pop star Justin Bieber was filmed lunging and shouting abuse at a photographer on Friday during an ill-fated stay in London which has gone from bad to worse after he collapsed on stage the day before.
The altercation, caught on camera and featured on popular celebrity news websites including TMZ, showed the 19-year-old get out of a van, try to move towards the unnamed member of the paparazzi and threaten him using several swear words.
He was reacting to the man's foul-mouthed criticism of him and his security team after the singer appeared to have made contact with the photographer as they moved towards the vehicle.
The bouncers held Bieber back, but the incident is likely to create yet more negative headlines for one of the world's biggest pop stars.
Bieber said he would go ahead with a scheduled Friday concert, the final of four gigs at London's O2 Arena, which had been in doubt after he collapsed on stage on Thursday after suffering from shortness of breath.
After a 20-minute break during which he was given oxygen by doctors, he completed his set but was later taken to hospital as a precaution.
"Justin has been released from the hospital after a check-up and while he's feeling a little under the weather, he's planning on going ahead with tonight's show," his spokesman said.
Since being discovered on YouTube in 2008, Bieber quickly built a huge following of mainly teenaged girls attracted to his clean-cut image, slick videos and catchy pop songs.
But the intense media spotlight which follows him around the world has clearly unnerved the "Boyfriend" singer.
Bieber has had several run-ins with paparazzi in recent years and took to Twitter this week to criticise the media for what he called fabricated stories about him during his stay in London, where he is performing his sold out "Believe" tour.
After the latest altercation, he returned to the micro-blogging site, where he has more than 35 million followers.
"Ahhhhh! Rough morning. Trying to feel better for this show tonight but let the paps get the best of me..." he wrote.
"Sometimes when people r shoving cameras in your face all day and yelling the worst thing possible at u ... well I'm human. Rough week.
"Not gonna let them get the best of me again. Gonna get focused on this show tonight. Adrenaline is high now. Gonna put it on the stage."
Thursday's onstage collapse was not the first for Bieber.
He suffered concussion during a concert in Paris last June after falling into a glass wall.
Bieber's illness came just days after he angered many fans by appearing for his first night at the O2 nearly two hours later than the advertised time.
The singer blamed technical issues for the delay, and said he was only 40 minutes behind schedule, but the media jumped on the story and the popular Sun tabloid referred to him in a March 7 story as "Pop brat Justin".
The tabloid attention has not been limited to the late show.
Newspapers described as "bizarre" his decision to wear a gas mask on a night out.
They also reported that Bieber, who celebrated his 19th birthday in London last week, tried to take 14-year-old Jaden Smith, son of actor Will Smith, to a club, where he was turned away, along with Bieber and his entourage.
Bieber took to Twitter and Instagram to vehemently deny the reports he tried to take underage Smith to a club, saying instead he was forced to leave the venue when the club's security guards behaved aggressively towards his fans who were lined up outside. (Reporting by Mike Collett-White; Editing by Sophie Hares)