Enyimba have secured a place and Rivers are set to join them once an outstanding fixture against Bloemfontein Celtic of South Africa is staged.
Celtic are trailing 2-0 from the first leg, but did not travel to Nigeria this week because they would not have had time to quarantine for seven days because of the coronavirus before the return match.
The playoffs pit Confederation Cup last 32 winners against Champions League last 32 losers like Enyimba, who were eliminated from the elite competition by Al Merrikh of Sudan.
Assuming Rivers qualify, the tie between clubs based 61 kilometres (38 miles) apart in southeastern Nigeria will bring together two of the sharpest forwards in the CAF club competitions this season.
Victor Mbaoma scored three goals for Enyimba in the Champions League and Godwin Aguda of Rivers matched that total in the Confederation Cup.
There are seven former African champions among the 30 clubs seeking passages to the group phase after the February 14 and 21 two-leg ties.
Two of them, Asante Kotoko of Ghana and Entente Setif of Algeria, meet in another appetising playoff in the African equivalent of the UEFA Europa League.
Kotoko won the African Cup of Champions Clubs -- forerunner to the Champions League -- twice and were runners-up five times while Setif also triumphed twice in the premier African competition.
Both clubs could suffer from rustiness as Kotoko played only two of four scheduled Champions League matches due to Covid-19 issues before dropping to the Confederation Cup.
Setif have yet to play in Africa as they received a preliminary round bye in the Confederation Cup, then a walkover when Renaissance of Chad failed to show.
Enyimba (NGR) v Bloemfontein Celtic (RSA) or Rivers Utd (NGR)
Platinum (ZIM) v Jaraaf (SEN)
Raja Casablanca (MAR) v US Monastir (TUN)
Gor Mahia (KEN) v NAPSA Stars (ZAM)Â
Asante Kotoko (GHA) v Entente Setif (ALG)
SONIDEP (NIG) v Coton Sport (CMR)
Stade Malien (MLI) v JS Kabylie (ALG)
Jwaneng Galaxy (BOT) v Orlando Pirates (RSA)
Primeiro Agosto (ANG) v Namungo (TAN)
CS Sfaxien (TUN) v AS Kigali (RWA)
Nkana (ZAM) v Tihad Casablanca (MAR)
Bouenguidi (GAB) v Salitas (BUR)
Young Buffaloes (ESW) v Etoile Sahel (TUN)
Al Ahly Benghazi (LBA) v DC Motema Pembe (COD)
RC Abidjan (CIV) v Pyramids (EGY)
Bye: Renaissance Berkane (MAR, holders)
First legs: Feb 14, second: Feb 21
Note: Winners qualify for group stage
Standout matches today