But transport bosses say they are confident teams will be able to catch up during the course of the project to ensure it is still completed on time.
The tram line is being extended to Brierley Hill, via Dudley, from Wednesbury in what is being hailed as a major boost for the region's transport links.
Work on the scheme has continued during the summer but progress has been slowed by the pandemic.
The demolition of the redundant railway bridge in Coneygree Road, Tipton, next month will mark another major step forward for the project.
The extended line is expected to open in 2023 and will feature 17 new stops, connecting with Dudley Port train station, Dudley bus station and the Merry Hill shopping centre. Works have also been taking place to extend both ends of the existing Metro line, in Wolverhampton and Birmingham.
A progress report said: "The Metro team are reporting a potential delay of six months to the completion of the project due to the impact of Covid and the delays to the Network Rail Agreement.
"However, they remain confident of recovering the programme over the next three years."
Dudley Council deputy leader David Vickers said every effort would be made to ensure the new line is delivered on time.
He said: "The pandemic is holding everything up all over the world. Social distancing has not only been on the spot but on our suppliers and partners, so it has taken an effect.
"It is running late by six months but we will make every effort to catch it up. It's in everyone's efforts interests to catch it up so we will be working hard to do that."
The line is viewed crucial for Dudley's economy as it will bring badly-needed improved transport links, allowing more people to travel sustainably to the town centre and the Merry Hill shopping centre.