The midfielder received treatment for eight minutes in the 2-0 defeat at Stamford Bridge after a heavy collision with Chelsea captain Gary Cahill.
Mason was left with a fractured skull, which required surgery at St Mary's Hospital.
Cahill and John Terry led a Chelsea delegation to visit Mason on Sunday, and Tigers captain Michael Dawson has also checked in on the 25-year-old.
A statement read: "The club can confirm that Ryan has been visited this morning at St Mary's Hospital by club captain Michael Dawson, club doctor Mark Waller, head of medical Rob Price and club secretary Matt Wild.
"Ryan has been speaking of the incident yesterday and will continue to be monitored at the hospital over the coming days where the Club will remain in close contact with Ryan, his family and the staff at St Mary's."
Tributes and well-wishes have poured in to Mason, with Chelsea head coach Antonio Conte, Real Madrid star Gareth Bale - a former Tottenham team-mate - and England striker Harry Kane among the stars to offer their support.
Hull said: "Ryan and his family have also been extremely touched by the overwhelming support they have received and would very much like to thank all of those who have posted such positive comments both on social media and in the press over the last 24 hours."