There was a time when Vijayan's main opponent in the party was the veteran V.S. Achuthanandan, a former Chief Minister. Jayarajan, 66, is different.
A two-time legislator and a former Kannur district party secretary, Jayarajan is now the rave of party members not just in Kannur but also in other northern districts like Kozhikode and Kasargode where the Communist Party of India-Marxist (CPI-M) remains a powerful force.
While Achuthanandan had a huge support base from the man on the street, Jayarajan's backing comes from within the rank and file of the CPI-M.
Party leaders admit that Vijayan has started to feel the heat, with Jayarajan almost achieving a 'cult' status, especially in the northern districts.
Everywhere in these districts, Jayarajan is omnipresent in the form of huge cardboard cutouts showing a personality cult rarely seen in the CPI-M.
He also has a huge following on the social media with groups like 'PJ Army' glorifying Jayarajan and keeping track of what he does.
Jayarajan's new status has come though he lost the Lok Sabha election to Congress candidate K. Muraleedharan, son of former Chief Minister K. Karunakaran, in Vadakara.
A fortnight back when Nigeria-based Kannur resident Sajan Parayil, 49, committed suicide after he failed to get clearance from Anthoor Municipality for his state-of-the-art Rs 16 crore convention centre, Jayarajan took a strong position against Municipality chief P.K. Shyamala, wife of CPI-M leader M.V. Govindan.
Jayarajan's image got a further boost in Kannur after the Vijayan government suspended four Muncipality employees for delaying the sanction.
This irked Vijayan as the Congress was demanding that Shyamala should face criminal action for the suicide.
Left thinker and analyst N.M. Pearson said the party was passing through one of its toughest times, after losing 19 of 20 Lok Sabha seats to the Congress-led United Democratic Front (UDF).
"When Vijayan took on Achuthanandan, he had the near full support of the party. But in Jayarajan, things will be different," said Pearson.
Adding to Vijayan's woes, Mumbai Police has registered a rape case against Binoy Kodiyeri, son of CPI-M Kerala Secretary Kodiyeri Balakrishnan, who is known to be close to the Chief Minister.
One reason why Jayarajan's stock is popular is his lifestyle. He is viewed as an accessible leader, in contrast to many others.
And unlike the children of many party leaders who are known to enjoy the good life, Jayarajan's son was recently seen working in a hotel.
The coming days will reveal whether or not Jayarajan emerges as a challenger to Vijayan.
( With inputs from IANS )