The Competition Commission said the merger of the two California-based companies "could severely inhibit the entry of a major new competitor, CTS Eventim, into the U.K. ticketing market."
Before the merger plan was announced, Live Nation had agreed to provide ticketing services for CTS' live music events and venues in Britain.
That arrangement promised to significantly increase competition in the market, the commission said.
It said possible remedies include prohibition of the merger, divestment of some of Ticketmaster' or Live Nation's U.K. operations, or require Live Nation to use CTS or another company to sell tickets for Live Nation's U.K. events.
The commission set an Oct. 29 deadline for interested parties to comment ahead of a final ruling.
Ticketmaster, based in West Hollywood, is the largest seller of tickets to live concerts and other entertainment events in the United States. It also owns an artist management company, Front Line Management, and a ticket-reselling company called TicketsNow.com.
Live Nation, based in Los Angeles, is the largest U.S. concert producer. It also owns entertainment venues and in January launched its own ticket-selling business, which currently competes with Ticketmaster.
CTS Eventim AG is based in Bremen, Germany.
On the Net: http://www.competition-commission.org.uk