Metrolink's new service to south Manchester will not start for at least another week due to problems with aligning new computer systems, Transport for Greater Manchester said.
In a statement the passenger transport executive said a "key part of last weekend's work to prepare the line for passenger service this week could not be completed.
"Engineers and technicians from Thales, the contractor delivering a new tram management system, will now need to re-schedule this part of the testing and commissioning for the coming weekend 2 to 3 July."
Philip Purdy, Metrolink director, said: "I am sorry that we're going to have to disappoint people this week but we have to make sure we have done all the testing and commissioning before we welcome passengers aboard."
Purdy added: "The new system has to 'talk' to the existing system. The problem is that the new system is as advanced as the current system is old, so it's a bit like connecting your modern PC to a Commodore 64 and making them work together at this higher level.
"We were able to do some preparation and commissioning this weekend but the available time didn't allow us to complete the integration testing of an upgrade.
"Frustratingly for us and our customers this upgrade then caused a fault on the existing system which meant we had disruption [on Monday] morning. We have done many similar upgrades in the past without any problems."
The new south Manchester line, with stops at St Werburgh's Road, Chorlton and Firswood, will give passengers a 15-minute link from Chorlton to St Peter's Square.