Project director Amanda Farrell says crews found a depression that turned into a hole (on Clarke Road near Seaview Drive) on Friday night.
She says the area has been fenced off and traffic has been temporarily closed in both directions while crews address the situation.
Farrell says she isn't sure of the depth of the sinkhole but it is a metre or two across and crews were filling it with cement overnight.
The three previous sinkholes opened up during maintenance on the tunnel boring machine below Clarke Road and frustrated drivers and residents.
The two kilometre-long tunnel is set to be finished this year and will end near an intersection (at Clarke Road and Como Lake Avenue).