The 19-year-old, who began his career with Arsenal, moved to Deepdale in 2012.
He could make his U's debut in Saturday's League One match against Bradford City.
Colchester boss Joe Dunne told the club's official website: "He's straight into the squad. We've monitored him and seen he hasn't been in their set-up so far this season. He's played behind-closed-doors matches for them, so he's fit and ready to go for us.
"Jeffrey is an attack-minded player, who wants to attack the box and is very much one who fits into our style of play. He's not afraid to cut inside and shoot from distance and I think we've been lacking that.
"We need to be attacking the box a bit more and I know he can do that. He wants to carry the ball and take people on one-on-one, so we're looking forward to working with him in the next few weeks."
Monakana has made 49 appearances for Preston, scoring six goals in the process.