The European Tour has reduced next week's Porsche European Open to 54 holes after host country Germany placed the United Kingdom on its travel red list.
The German Government tightened restrictions on travel for British citizens earlier this week after the country’s Public Health Institute designated the UK as a virus variant area of concern.
As well as cutting the tournament to three rounds, the European Tour has moved the event to run from Saturday to Monday, rather than the usual Thursday start, to ensure those competing and support staff will not have to quarantine.
A European Tour statement said: "Next week's Porsche European Open in Germany will now take place over 54 holes and be played from Saturday June 5 to Monday June 7.
"The tournament, at Green Eagle Golf Courses in Hamburg, was originally scheduled to begin on Thursday June 3 and be played over 72 holes, but the late change has been made after the German Government’s decision last week to place the United Kingdom on its travel 'red list’.
"This has meant almost a third of the scheduled 156-player field, along with a similar number of caddies and a significant number of European Tour Productions and European Tour staff, would have been unable to enter Germany without observing a mandatory quarantine period if they had not been outside the UK for a minimum of 10 days.
"Moving the starting date of the Porsche European Open back two days to Saturday June 5 allows the vast majority of those people affected to spend that requisite time outside of the United Kingdom both during and after this week’s Made in Himmerland tournament in Denmark, before crossing the border into Germany next Friday."
Major champions Martin Kaymer and Henrik Stenson, current top-20 players Paul Casey and Abraham Ancer, as well as Northern Ireland's Cormac Sharvin and Jonathan Caldwell, are among the notable names currently due to compete in Hamburg.
European Tour chief executive Keith Pelley said: "The significant travel changes announced last week meant it was simply impossible for us to start the Porsche European Open as intended a week today without unacceptably damaging the field and the integrity of the tournament.
"Over the past year we have had to react to numerous changes at short notice and our ability to do this has unquestionably been down to the flexibility of our players, caddies, staff, broadcaster partners and sponsors.
"This is another wonderful example of everybody working together pragmatically to find a solution.
"We are therefore extremely grateful to everyone involved, particularly Porsche and promoter U.COM Event for their adaptability, understanding and unwavering support in making these fundamental changes so close to the tournament, with so much of the infrastructure already in place.
"That has enabled us to not only provide vital playing opportunities for as many of our members as possible, but also to showcase this prestigious event, and Germany, properly to our global television audience."