McPartlin's co-presenter was pictured in Chiswick today after it emerged he is to consider options on the future of his TV career.
A spokesperson for the pair revealed that this week’s Saturday Night Takeaway would be cancelled as McPartlin re-entered rehab.
“He’s very upset and needs time to make any decisions, which is why this weekend’s episode of Saturday Night Takeaway was cancelled,” a friend of the pair told The Sun.
“ITV understood that the show couldn’t go ahead without Dec and that he’ll have to make a final decision about what happens.”
A separate source added: “Dec is absolutely devastated of course, but he is also incredibly supportive.
“They are much more than co-stars. They’re best friends.”
Ant and Dec have been ITV’s most successful presenting duo for the last 20 years, and were due to host the new series Britain’s Got Talent following the finale of Saturday Night Takeaway.
In a statement yesterday, ITV confirmed that this week's Saturday Night Takeaway would be cancelled, while the remaining two episodes will be "reviewed" this week.
“ITV has taken a joint decision with Ant and Dec’s team not to broadcast Saturday Night Takeaway this weekend," the statement read.
“We will be reviewing options for the last two episodes of the series (March 31 and April 7) which would not feature Ant who is taking time off to seek treatment.
The spokesperson concluded: “We very much hope that he gets the help that he needs."
A spokesman for McPartlin told The Sun: "Ant has decided to go back into treatment and step down from his current TV commitments.
“He has spoken with Dec and ITV today and asked for time off for the foreseeable future.
“As such ‘Saturday Night Takeaway’ will not be going ahead this Saturday."
McPartlin was arrested at around 4pm on Sunday after failing a roadside breathalyser test following the crash involving two other cars, which left a four-year-old girl needing medical attention.
He reportedly lost control around a bend, causing his car to veer into oncoming traffic before hitting restaurant owner Faheem Vanoo’s Mini and another car behind.
A Metropolitan Police spokeswoman said that the presenter was "taken to a south London police station for questioning and has since been released under investigation" and that inquiries continue.