Depending on the severity of the tear, exercise is possible and even encouraged. Muscle tears fall into the categories of 1st degree (slight tear), 2nd degree (partial tear) and 3rd degree (complete rupture). If you have sustained a 3rd degree tear, this is most usually a surgical situation, requiring physical therapy post injury.
A 2nd degree tear deserves a little rest until normal walking is painfree. You'll know it is a 2nd degree tear, because often you will feel a muscular defect (small drop off in the muscle) right where the tear occurred. Once you are able to walk painfree, feel free to add biking or walking on a flat treadmill as activity, but stay away from toe-ups or squatting activities.
On the other end of the spectrum, a 1st degree tear can endure exercise and in fact, activity is encouraged to prevent scar tissue from developing inside the muscle tissue. Activities that utilize the calf muscle, but don't stretch it to its full length are great exercises to work on while recovering from a gastroc/soleus (calf) muscle tear. A great example is biking - a stationary bike would be best. Walking is fine, but you may have pain on hills, so keep to a flat surface. Stay away from squats with weights or toe-ups - anything that stresses the calf muscle until you have no pain.
Once your pain is gone, begin with light calf muscle stretching on a slant board and add towel scrunches for some beginning strengthening. A towel scrunch is where you sit with a towel at your feet on a wood or tile floor and "scrunch" up the towel using your toes - it isn't easy! After mastering those activities, add isometric wall pushes where you push your toes against a wall - last but not least would be a full weight bearing toe up - don't add weights until you are fully healed (6-8 weeks)! All else fails - ask me about finding you a local physical therapist!