Andy Murray is to undergo tests following his withdrawal from the Miami Open, it is understood.
The world number one pulled out of this week's Masters series tournament on Saturday because of a right elbow injury.
Murray has stayed in Miami, where he has a second home, but will fly back to London on Wednesday night.
He will have tests on his elbow and has been told to rest for the next week or so, with the Scot understood also to be a little under the weather.
Murray was diagnosed with shingles following his shock fourth-round exit from the Australian Open in January but insisted he was fully recovered when he returned to action in Dubai in February.
He won that tournament but then suffered another surprise defeat to Canada's Vasek Pospisil in his first match in Indian Wells earlier this month.
Despite Murray's difficult start to the season, he has substantially extended his lead at the top of the rankings because of the struggles of main rival Novak Djokovic.
Djokovic failed to defend his titles in Australia and Indian Wells and has also withdrawn from Miami - where he has won the title the last three years - with an elbow injury.
It now seems highly unlikely that Murray will take part in Great Britain's Davis Cup quarter-final against France in Rouen in a little over two weeks.