The 23-year-old has made a bright start to the new season, scoring twice and providing two assists across five starts and four substitute outings in all competitions.
Matondo set up Cyriel Dessers for the only goal in Rangers' 1-0 home win over Motherwell in the Scottish Premiership on Sunday, but he was forced off shortly before half time due to injury.
The Wales international is the latest name to be added to a lengthy injury list after Banfield confirmed that he will be sidelined for a lengthy period.
Speaking at a press conference on Tuesday ahead of Rangers' Scottish League Cup quarter-final with Livingston on Wednesday, Banfield said: "Rabbi looks like (he will be out for) six weeks with his knee.
"With injuries, we know we have built a strong squad and it is for players to step up and help send us to Hampden Park.
"We will always have bumps along the way but it is up to us to continue to push and prepare the team."
Matondo will now join Danilo (fractured cheekbone), Nicolas Raskin, Tom Lawrence, (both calf), Todd Cantwell and Kieran Dowell (both knee) in the treatment room.
Following an underwhelming start to the new season, Michael Beale's side appear to have turned a corner in recent weeks, winning each of their last three matches without reply against St Johnstone, Real Betis and Motherwell.
Rangers are considered the favourites to go all the way in the Scottish League Cup after rivals and holders Celtic were surprisingly eliminated in the second round by Kilmarnock, and Banfield has highlighted the club's need to "focus on winning the next trophy."
"It is a three-game week and we need to be ready and prepared for the next match," sad Banfield. "We want to win again and be at Hampden Park for the semi-final.
"The history of Rangers is about winning trophies, that is always the focus at this club is to focus on winning the next trophy.
"The fans give us great support every match, we know they will be backing the team again tomorrow night. We will keep working hard to be successful. We are definitely heading in the right direction."
Rangers, who were beaten by Celtic in the final last season, have won 10 of their last 11 meetings with Livingston in all competitions, including a comfortable 4-0 league win at Ibrox in August.