United have got a problem with Nermanja Vidic serving a suspension after being sent off against Chelsea, but Gibson believes that Sir Alex has the back-up he needs to win this one.
Jonny Evans and Chris Smalling are one option, Wes Brown and John O'Shea is another.
"It is a big blow to lose Vidic, but we have got players capable of stepping in and doing a job," Gibson told Sky Sports.
"Jonny Evans is back, Wes Brown is there and John O'Shea can play at centre-back so I think we have got players capable of stepping in and covering.
"It has to be the biggest game still for us.
"Obviously City's rivalry is going up because they are pushing up and challenging us, but Liverpool is still the biggest one for us."