He further expressed hope that Rouhani will win the election by a landslide so he could improve the country's future.
Eshaq Jahangiri, senior vice president under Rouhani, dropped out, leaving just four candidates in the race ahead of Friday's vote. "This great ideal can only be achieved by changing the status quo".
Rouhani, a pragmatist who has eased Iran's worldwide isolation and now faces mostly hardline conservative challengers for the presidency, told supporters he needed a stronger mandate to liberalise Iranian society and get opposition leaders freed.
"Not all of Qalibaf's supporters will move to Raisi, but he does provide some capacity for conservatives to unite", said Suzanne Maloney, an Iran scholar at the Brookings Institution in Washington.
There was no immediate reaction from Rouhani.
That held true in 1997 with the election of reformer Seyyed Mohammad Khatami, who threw his support Monday behind Rouhani. They included Mostafa Aqa-Mirsalim, Mostafa Hashemitaba, Es'haq Jahangiri, Mohammad Baqer Qalibaf, Seyyed Ebrahim Raisi and Hassan Rouhani. That is not to say, however, that all of Qalibaf's supporters will automatically vote for Raisi.
It's unclear how much support Qalibaf enjoys today.
Another survey by the Iranian Students Polling Agency last week showed that, in a head-to-head contest, neither Rouhani, nor Raisi would garner the 50 percent of votes needed to win in the first round and avoid a run-off. The polls show he is seen as far more capable than his challengers both to improve Iran's foreign relations (55 percent for Rouhani, 22 percent Ghalibaf, and 6 percent Raisi) and to remove worldwide sanctions (48 percent Rouhani, 21 percent Ghalibaf, 7 percent Raisi).
A bruised Rouhani may struggle to secure enough votes to avoid a second ballot, prompting some analysts to predict he might lose in a run-off against Ebrahim Raisi, a former prosecutor Khamenei has helped build up, appointing him a year ago to oversee Iran's largest shrine and its charitable foundation. He was later promoted by Ayatollah Khamenei as the custodian of Astan Quds Razavi, a foundation that manages donations to the country's holiest shrine in the city of Mashhad. He already has the support of two major clerical bodies that declined to endorse anyone in the last presidential election. It was the urgency of this political balance, both domestically and internationally, that provided the raison d'être of Mr. Rouhani's victory in 2013. Some also have speculated that Qalibaf could serve as a vice president in Raisi's administration, in exchange for his support.
Rouhani has stabilised the Iranian economy and brought down inflation but unemployment is high and his opponents have questioned whether his administration has done enough to bring tangible economic benefits to the country.
Qalibaf's withdrawal gave "strength and momentum to Raisi's campaign" at a time when voter interest is peaking, said Mauriello. "In Tehran, his votes will go mainly to Rouhani but outside Tehran his supporters will vote for Raisi".