( CNN ) -- New Kids on the Block singer Jonathan Knight left fans confused and concerned Thursday when he walked off stage in the middle of a concert in New York . According to reports , the five-member boy band was performing a mix of their old hits from the late '80s and early '90s , along with music from their new album , `` 10 , '' when onlookers noticed that Knight seemed out of place . HollywoodLife.com 's Emily Longeretta was in the front row , and wrote on the celebrity website that Knight `` seemed out of it . While the men started their choreographed dances , Jonathan stood uncomfortably in the background -- actually just standing and texting on his phone during the performance . '' Billboard.com also reported that Knight seemed `` visibly out of sync . '' He did n't join in when NKOTB got fans ' arms waving with the memorable 1989 single `` Hangin ' Tough , '' and kept to the back of the stage as the other members worked to entertain the crowd . The other members -- Knight 's brother , Jordan , plus Danny Wood , Joey McIntyre and Donnie Wahlberg -- put their arms around him for support . Yet when Jordan said his brother was going to sing `` Survive You '' from `` 10 , '' Knight made an attempt at the song , and then walked off the stage . The rest of NKOTB went on singing as fans chanted for Knight 's return , but he never came back . The singer has been vocal in the past about his struggle with anxiety , prompting speculation that that 's what he was facing Thursday night . On his Twitter account , Knight appeared to give fans a simple apology , tweeting `` I 'm sorry ... ... '' on Thursday evening . Earlier that day , he posted the hashtag `` I feel naked , '' perhaps indicating his state . NKOTB , one of the heartthrob boy bands of the late '80s and early '90s , came off a lengthy hiatus in 2008 , and have issued two albums since then . They 're also slated to go on a tour this summer with 98 Degrees and Boyz II Men , and Jonathan 's performance Thursday had some questioning how many members of the group would make it . But Wahlberg , for one , seemed unruffled . `` To recap , '' he tweeted after the New York event . `` Joe was especially dazzling ! Jordan was especially amazing ! Danny was especially solid & Jon was especially shy ! # Allsystemsnormal ''
Jonathan Knight walked off stage in New York on Thursday . Those in attendance said he seemed out of it during the show . After being asked to sing , he left and did n't return . Knight later posted an apology on his Twitter account .