British number one Heather Watson has been diagnosed with glandular fever, the Lawn Tennis Association confirmed earlier today.
Watson had been ordered to rest following her exit from the Miami Masters last week after complaining of fatigue.
After having blood tests in Miami, doctors have concluded that Watson has the virus but could not put a timeline on her return to the court.
In a statement on the LTA's official website Watson confirmed that she has been ordered to take a break from tennis to recover from the illness.
She said: "I had to do some blood tests after Miami and the results have shown that I have traces of glandular fever in my system. There is no prescription for this other than complete rest but the good news is that the doctors have told me I am at the tail end of the fever.
"This means I have been trying to compete through the symptoms for some time. I have been struggling with both training and playing matches and felt so tired and exhausted for months but now that the doctors have found the cause of this, it explains everything that has been happening to me physically and mentally.
"I am actually relieved to know what is wrong so that I can get myself on the mend. I hope to recover as soon as possible by resting my body and getting lots of sleep. I already feel better from being at home for a week, and am looking forward to getting back on tour soon."
Watson is on the verge of losing her position as British number one to Laura Robson after she progressed in the Family Circle Cup with a straight-sets win this morning.