The man wearing an Afghan National Army uniform shot at International Security Assistance Force (ISAF) service members Monday, the coalition said.
It did not say whether the shooter was killed or captured.
If the shooter is confirmed to be a member of the Afghan army, the attack will be the first of the so-called "green-on-blue" insider attacks this year, in which Afghan army, police or gunmen in their uniform open fire at their international partners.
A total of 405 foreign soldiers were killed in Afghanistan last year. Of the total casualties, 58 coalition soldiers were killed in green-on-blue attacks.
The Taliban have regularly claimed responsibility for green-on-blue attacks, saying their men have infiltrated into the ranks of the Afghan army and police to kill foreign soldiers.
Fifty countries are contributing 100,000 soldiers in Afghanistan with over 68,000 of them American, followed by 9,500 from Britain.