Chelsea captain Cesar Azpilicueta has been discharged from hospital after suffering a concussion during Saturday's home defeat by Southampton.
Azpilicueta lay motionless on the pitch after being struck in the face by Sekou Mara as the Saints substitute attempted an overhead kick.
The Spain defender, 33, received oxygen treatment for several minutes before being taken off on a stretcher, though he was conscious as he left the field.
Chelsea said he was "recovering well".
In a statement on Tuesday, the Blues added: "The club's medical team are closely monitoring Cesar's condition, adhering to the important concussion protocols in place to ensure his safety.
"Cesar observed training today, before he starts working towards returning to the pitch."