Lee Latchford-Evans has tested positive for Covid and will miss remainder of the Steps tour.
The news comes just as bandmate Faye Tozer returns to the stage after completing her government issued period of isolation.
Faye, 46, was forced to miss several dates of the What The Future Holds after contracting the viral disease earlier this month.
Steps shared to "disappointing news" of Lee's positive test result with their fans on Saturday afternoon.
Sharing a statement on the official Instagram page for the band, Faye, Ian 'H' Watkins, Claire Richards and Lisa Scott-Lee confirmed they would continue without Lee for the final three shows.
"We are sorry to report that in disappointing new, Lee has this morning tested positive for Covid-19 which means he is now isolating and will unfortunately be absent for the remainder of the 'What the Future Holds' tour," they told their 91,700 followers.
The Tragedy singers continued: "We intend to carry on with the remaining three shows while the rest of us test negative."
The band then went on to confirm the good news that "in line with government guidelines", Faye has now completed her isolation and will be joining the group on stage at The 02 on Saturday night.
Faye had been "baffled" by her positive Covid case earlier this month - stressing she had been very careful and followed all precautions.
"Thankful for our daily testing to have been able to recognise it and so the show can still go on," she said at the time.
"Please give the guys the biggest love as they continue to smash the shows and I hope to be back soon."
Elsewhere in Steps most recent statement, the group wished Covid-stricken bandmate Lee well as he recovers from the contagious disease.
"We hope you will join us in wishing Lee a speedy recovery," they wrote, signing off as Claire, Faye, H and Lisa.
Steps - who first officially reunited back in 2017 - released their sixth studio album, What the Future Holds, last year but Covid led to delays on touring their first release on a new record label.
Missing the final few shows will come as a blow to Lee who, prior to his positive test result, had been enjoying a successful year in both his career and family life.
In July, the singer and wife Kerry-Lucy shared the joyous news that they had become parents together for the first time.
The 46-year-old took to Instagram to welcome his "perfect rainbow baby" to the world as he celebrated becoming a father.
"Welcome to the world baby boy," Lee captioned a black and white image on Instagram of his newborn child's hand clutching his.
"Me & your mummy @kerrylucyinsta are so in love! You’re everything we could have wished for & more, Our perfect rainbow baby," he added, including a blue love heart and rainbow emoji with his sweet words.
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