McCoy played the Seventh Doctor from 1987 to 1989.
On Sunday (8 May), Gatwa was revealed as the next actor in line for the iconic role, taking over from Jodie Whittaker in 2023.
In support of the news, McCoy shared a video welcoming the Rwandan-Scottish star to “our unique club: the Doctor Who club.”
Elsewhere in the light-hearted clip, the veteran actor stated that he was anticipating watching Gatwa defeat some enemies during his tenure as The Doctor.
He said: “I’ll be delighted to watch you take on the Daleks, the Cybermen, the Weeping Angels, and the critics.”
On Wednesday (11 May), the Sex Education actor posted his own video, directly responding to McCoy’s message.
“Sylvester McCoy, thank you, thank you, thank you, thank you so much for your beautiful message,” Gatwa said on his Instagram Story. “It means the absolute world, especially coming from a fellow Scot.”
Nodding to McCoy’s comment about the critics, he continued: “I am so looking forward to facing all of those foes, especially the last one that you mentioned.
“The support from you and all the other Doctors has just filled me with the strength that I will be able to do that.”
Gatwa ended the message by thanking McCoy and the other Doctors for welcoming him into the family.