It is the Lions' second major injury blow in less than 24 hours after Ireland flanker Stephen Ferris suffered a tour-ending knee injury.

Cardiff Blues prospect Halfpenny, at 20 the squad's youngest player, is set to return home later this week.

He sustained a thigh muscle injury in training on Monday, and now requires three to four weeks of rehabilitation.

The Lions have decided not to replace him as head coach Ian McGeechan feels he has enough existing cover in the squad.

Halfpenny, who made his Test debut against South Africa barely seven months ago, was a late arrival on tour.

He remained at home for intensive treatment on a thigh injury, before being being given the all-clear to link up with the squad last week.

He started the Lions' third tour game against the Cheetahs in Bloemfontein four days ago.

"Leigh unfortunately hurt his right thigh muscle during Monday afternoon's training," said Lions head coach Ian McGeechan.

"Following a medical assessment, it was decided that he should undergo a scan to determine the extent of the injury.

"He had the scan on Tuesday morning that confirmed a presence of a further muscle injury to his right thigh which will require three to four weeks of rehabilitation which means he will miss the rest of the tour.

"I am especially disappointed for Leigh, as he has worked so hard to come back from the setback at the start of the tour, but he has proven his strength of character by the way that he is handling the news. We wish him a speedy recovery.

"Leigh will travel with us to Cape Town (tomorrow), and then return to the UK to continue his rehabilitation with Cardiff Blues."

Lions manager Gerald Davies added: "We are obviously very disappointed that Leigh has sustained a further injury.

"And we understand that this must be particularly frustrating that this has happened a second time, especially for a young man embarking on his rugby career, but we wish him well for his rehabilitation."

Halfpenny won six caps this season, scoring four tries, and also touched down during Blues' crushing EDF Energy Cup final victory over Gloucester at Twickenham in April.

In addition to his prowess on the wing, he also offered the Lions a goal kicking option, suggesting he might have challenged for a Test squad bench role.

Halfpenny's knockout blow comes with the Lions still reeling from losing Ireland Grand Slam winner Ferris.

The Ulster forward will be out for between four and six weeks after seeing his Lions dream shattered.

Wales captain Ryan Jones, a tour replacement on the last Lions trip four years ago, will take Ferris' place and is expected to arrive in Cape Town tomorrow.

Halfpenny and Ferris join four other players who were selected by McGeechan, only to be ruled out.

Scrum-half Tomas O'Leary, centre Tom Shanklin and hooker Jerry Flannery all suffered serious pre-tour injuries, while Munster flanker Alan Quinlan missed out due to a 12-week ban imposed after he was cited for foul play during the Heineken Cup semi-final against Leinster.

The Lions play their fourth tour game tonight, tackling the Sharks in Durban after beating the Royal XV, Golden Lions and Cheetahs.