World No. 18 Arthur Fils took a medical timeout during his fourth-round Masters match in Miami against Alexander Zverev.
The French player requested a physiotherapist after the first set, which he lost 3-6.
Fils reportedly commented on his back issue, stating it was affecting his forehand and return.
After the medical timeout, Fils secured an early break and is currently leading in the second set.
Rupert Hartwell 
Adrian Whitmore