Today, the analysis of the risk of developing cardiovascular complications in patients with essential hypertension (EH) following recovery from novel coronavirus infection (COVID-19) is relevant. The value of leukemia inhibitory factor (LIF) and its soluble receptor (sLIFr) in EH progression has been shown, along with the relevance of circadian approaches to assessment of the contribution of pro-inflammatory cytokines to the pathogenesis of acute cerebrovascular accidents (CVA). The study aimed to compare alterations of the LIF and sLIFr levels during reconvalescence after COVID-19 and influenza in patients with stage II EH, to determine the features that are important for the development of acute CVA, and to analyze the associations with circadian rhythms. The study was conducted in four phases (n = 180; age 55–60 years): (1) 6–8 months before COVID-19; (2–3) on day 10–14 after primary or recurrent COVID-19; (4) on day 10–14 after influenza. In each phase blood levels of LIF and sLIFr were determined by enzyme immunoassay at 7.00–8.00 h and 19.00–20.00 h, in 12 patients in four phases — at 7.00–8.00 h, 12.00–13.00 h, 19.00–20.00 h, 23.00–1.00 h throughout three days. It has been demonstrated that patients with EH show elevated LIF and sLIFr levels relative to healthy individuals in all time points (р ˂ 0.001) and significantly elevated levels at 19.00–20.00 h (р ˂ 0.001). The analysis of the relationship between circadian rhythms and blood levels of LIF, sLIFr in patients with stage II EH post COVID-19 and influenza has revealed similar changes in the form of the larger increase in sLIFr levels at 19.00–20.00 h (the ROC analysis data has shown predictive value for developing acute CVA within a year after СOVID-19 in cases of the value increase above 7100 pg/L at 19.00–20.00 h). The principles revealed actualize further investigation of the effects of the LIF/sLIFr complex associated with the EH progression after acute infectious diseases.