Sharif left for the UK for purported medical check-up amid chaotic political scenes by the opposition demanding his resignation after his daughter and two sons were mentioned in the Panama Papers as having secret offshore companies.
Pakistan Tehreek-e-Insaaf leader Imran Khan is consulting other parties for a joint possible protest outside Sharif's residence in suburbs of Lahore and Zardari's PPP joining the agitation that may make things difficult for the government.
Interior minister Nisar Ali Khan rejected the impression that Sharif was in tight corner and needed Zardari's support.
"For the last three weeks, his (Sharif) health has deteriorated for which the prime minister had to travel," he said at a press conference in Islamabad.
More From This Section
"In this country some people cannot even get ill as rumour-mongers keep on politicising the issue," he said.
Earlier, Sharif departed for London for what the government said was a "routine medical checkup, which was repeatedly postponed due to his official engagements over the past few months".
He had later addressed the nation and also promised to set up a commission to probe any wrongdoing.
However, the formation of the commission was delayed as the opposition rejected it.