Opening bat Hendricks brought up his third fifty of the season off 91 balls before ending unbeaten on 64 off 121 deliveries with 11 fours as the Knights stretched their lead to 204 runs.
The players left the field three balls before the scheduled tea break when heavy rain curtailed proceedings. The rain did not abate sufficiently to allow play to continue as 37.3 overs were left unbowled because of the bad weather. Play will start half-an-hour early on day four to try and make up the deficit.
Hendricks and Boeta Dippenaar (35 not out) combined for an unbroken third-wicket partnership of 61 after Rilee Rossouw had blazed his way to 20 off 23 balls before he drove a delivery from seamer Chris Morris to Neil McKenzie at mid-off.
Paceman Johan van der Wath had earlier returned figures of 4-79 while seamer Ryan McLaren chipped in with 3-74 as the Knights bowled the Lions out for 280 with the Knights taking a 58-run lead on the first innings.
Michael Erlank (14) and Hendricks then put on 29 runs for the first wicket before the left-handed Erlank was trapped leg-before by medium-pacer Zander de Bruyn with what proved to be the last ball before lunch.
The Lions began the day on 243 for seven before Morris (7) and Thami Tsolekile took the score to 264.
Morris departed in a rather unfortunate fashion when he pulled a short ball from offspinner Werner Coetsee and the ball rebounded off the short-leg fielder Erlank before popping up to allow keeper Morne van Wyk to complete the catch.
Pumelela Matshikwe (0) and Eddie Leie (4) departed soon after with Leie becoming Van der Wath’s fourth victim when he was bowled.
Tsolekile was left unbeaten on 35 off 97 balls.