Without the funding, the bus network in the region would risk “significant service reductions”, which the report said could cause “serious social and economic suffering” for residents and businesses.
It also raised fears the lack of funding could create an “unstable network” while the authority tries to deliver a franchised bus network.
The report said: “Whilst TfWM subsidises around 12 per cent of the network through tendered contracts, a further significant portion (around 30 per cent) of the network is at risk and fares face steeper increases.
“Continued grants also helps to mitigate any significant commercial increase in fares by bus operators as we transition from a de-regulated system to a franchised system.”
The WMCA board will meet on Friday. If approved, the scheme will be extended to 31 March 2027.