Speaking on Good Morning Britain, the presenters questioned why the Prime Minister was not facing the public more often.
Addressing political expert guests, Reid said on Tuesday: “I just wonder, I haven’t seen Boris very much.
"Where is the Prime Minister at the moment?"
While Morgan took to Twitter to call out Mr Johnson directly, writing: "Where are you, Prime Minister?"
Mr Johnson appeared last Wednesday for PMQs, where he faced his second showdown with Sir Keir Starmer after recovering from Covid-19 and returning to work.
The Prime Minister spent three nights in intensive care at St Thomas’ Hospital in London in April.
GMB guest Andrew Pierce said Mr Johnson had suffered "a very serious dose of coronavirus so he's probably not 100 per cent".
He also has recently become a father after his fiance Carrie Symonds gave birth, although it was reported he would delay his paternity leave.
Since returning to work on April 26, Mr Johnson has led the daily Downing Street press conference twice, given one Prime Ministerial statement to the Commons and appeared at PMQs twice.
His announcements about the lockdown easing have been made in pre-recorded television broadcasts.
Reid said she did accept the Prime Minister "has a new baby” and noted the impact of post-coronavirus fatigue.
While Morgan said that the issue was the lack of transparency from Number 10 Downing Street over Mr Johnson’s public appearances and the pressure his absence places on other cabinet ministers.
He said: “The fact he is not visible and centre-stage means we are now reliant on other ministers.”
He added: "Be honest with the public, if he's ill or feeling rough, be honest with the public… They’ll understand.”
— Good Morning Britain (@GMB)
Former prime minister Gordon Brown appeared on GMB on Tuesday and said that Mr Johnson needed to "get a grip".
Mr Brown told the programme that he would have been “laughed out of court” had he given just one official coronavirus statement to Parliament over his response to the global financial crisis in 2009.
Mr Johnson's spokesman on Monday confirmed health reasons were not behind his failure to appear more often.
GMB has been boycotted by Government ministers for over three weeks.