Sundowns won the first leg 2-0 in Equatorial Guinea.
"I don't think Equatorial Guinea's Leones could easily score three here. I don't say they can't score three, but I think we have a goal here on Wednesday," Mosimane said.
"We have a goal. I don't think they can score four goals against us. It will be naughty [of us]."
Meanwhile, Mosimane confirmed Liberian forward Anthony Laffor is available for the game, which is scheduled to kick off at 19h00.
"Laffor is ready, he is fit. Unfortunately I wanted to throw him [on against SuperSport United in Sunday's Tshwane derby] on in the last 10 minutes but we were worried by crosses and set-pieces, hence we put in Wayne Arendse."
Mosimane, however, is without first-choice goalkeeper Denis Onyango (knee) through injury, as well as Brazilian defender Ricardo Nascimento (hip), out-of-favour winger George Lebese (knee) and striker Thokozani Sekotlong (ankle).
Midfielder Tiyani Mabunda also faces a late fitness test.