Martin McGuinness' surprise withdrawal from a ministerial visit to China was due to a health scare, officials have said.
The Deputy First Minister attended a Belfast hospital earlier this week after a medical issue arose.
It was the reason for the Sinn Fein MLA pulling out of this week's high-profile mission to China.
Last Friday the Executive Office released a statement saying Mr McGuinness would not be travelling to the country as expected.
His absence had been blamed on "unforeseen personal circumstances".
The Belfast Telegraph has chosen not to publish exact details of the matter out of respect for his privacy.
Last night Sinn Fein president Gerry Adams confirmed Mr McGuinness had withdrawn from the China visit "to enable doctors to conduct a medical assessment".
He said: "I'm sure everybody who values his work will send best wishes to Martin, (his wife) Bernie and their family.
"I met with Martin as normal at Stormont on Monday.
"I have been in regular contact with him since and he is totally committed to fulfilling his duties."
A spokesman for the Executive Office said: "The Deputy First Minister withdrew from a planned visit to China this week on medical advice and to enable doctors to conduct a medical assessment.
"Martin McGuinness is fulfilling his responsibilities as Deputy First Minister, working with his departmental political advisers.
"There has been no disruption to the work of the Executive Office during this period."
There was surprise last Friday when it was announced that Mr McGuinness would not be heading to China. Instead, First Minister Arlene Foster travelled alone on the four-day visit.
Yesterday she officially opened the Executive's Bureau at the China World Trade Centre in Beijing.
Both the Executive Office and Sinn Fein have refused to elaborate further on the reasons for his absence.
The Executive Office had also refused to say whether Mr McGuinness was working at Stormont this week.
On Wednesday, however, Mr McGuinness's name appeared alongside that of Mrs Foster on an Executive Office Press release paying tribute to Ulster GAA official Danny Murphy, who had passed away.
And last night his name was on a joint Executive Office Press statement announcing plans for high quality office accommodation for Ebrington, Co Londonderry.
Mr McGuinness was quoted in the Press statement.
Although Mr McGuinness is one of Northern Ireland's most high-profile figures, he is very protective about his personal life and his family's privacy.
He married his wife Bernadette in 1974.
They have four children, two girls and two boys, but his family are kept well out of the public spotlight.
Mr McGuinness is a member of the Pioneer Total Abstinence Association, meaning that he does not drink alcohol.
He previously revealed that he has suffered from tinnitus - a constant ringing in his ears.
Speaking earlier this year, he said: "I have had tinnitus for roughly the last 10 years. I don't know what caused my tinnitus but I started to become aware of a very low ringing noise in my right ear, which is now constantly there.
"As anyone who has tinnitus knows, it's not something that you can ignore and you have to deal with it on a daily basis."
Mr McGuinness said it had limited impact on day-to-day life or his work and that family, friends and work colleagues were very supportive.
It is the second medical incident to affect a senior Northern Ireland politician in recent times.
In May 2015 then First Minister Peter Robinson was rushed to hospital after suffering a heart attack.
Mr Robinson had to have stents inserted following the incident.
He later said his health issues were nothing to do with the stress of his job, but blamed his diet and lack of exercise.
"I blame myself and nobody else but myself," Mr Robinson said last year.
"The last emails that I was sending were at about four minutes to four in the morning and my men were timed to come at 7.30 to pick me up on that Monday morning, even though it was a bank holiday.
"If you looked at my diet you would just cringe - it's all around snacking and fast foods and all the things that you shouldn't do.
"Exercise? You're picked up from the door and dropped at the door, so it's all the worst lifestyle things."
Mr Robinson said he was given three stents that helped the flow of blood around the heart,and had a further procedure several days later.