Is it possible to drive an automatic car using left foot only?

Yes it's very possible. Normally mail persons drive this way sitting on the right seat. It is simple to do that same thing in the left seat. Normally if you have the use of the right foot though it is the safest to use the right. However if it is unavailable, I see no reason the left couldn't be used except slightly less cooridination would be the problem. You would have to drive accordingly in this case.