The Wales captain spent 11 years with Arsenal between 2008-19 which included two FA Cup final-winning goals for the Gunners.
But Ramsey, 32, reignited his north London rivalry with old foes Spurs after Johnson made the big-money switch from Nottingham Forest last Friday.
When asked about Johnson’s transfer, Ramsey quipped: “I wish it weren’t to Tottenham!”
Ramsey has linked up with Johnson for Thursday’s friendly with South Korea and a must-win Euro 2024 qualifier in Latvia next Monday.
And the Cardiff midfielder reckons ‘scary’ Johnson, 22, can scale new heights under new Spurs boss Ange Postecoglou.
Ramsey added: “It’s a brilliant move for him. The potential he has is quite scary and hopefully he can take those next steps and go to the next level.
“He’s going to be important for Wales as well. He’s going to be huge for us over the years to come and we’re all excited that he has another platform to go on and improve himself again.”
Ramsey was also the subject of a summer move after terminating his Nice contract to return home to boyhood club Cardiff.
The ex-Juventus and Rangers has scored twice for the Bluebirds this season but his latest effort could not prevent a 3-2 Championship loss at Ipswich on Saturday.
But Ramsey, who turned down a lucrative offer from Saudi Arabia, says he has been rejuvenated on the pitch because he is closer to his family of wife Colleen and three children rather than living on his own abroad.
Ramsey said: “I just feel like a weight has been lifted off my shoulder. I’m feeling a lot more free. That definitely helps on the pitch.
“It has been difficult being away from the family but you need that balance right to be able to enjoy every aspect, and I feel like I’m enjoying every moment now.
“I’m looking forward to doing the school run, having three boys screaming in the car in the morning. I’m glad they’re going back to school!
“I’m absolutely buzzing to be back and getting stuck into the family things as well.”
Ramsey once again pledged his support to under-fire Wales boss Robert Page after a woeful run of one win in 12 internationals.
He added: “We’re all behind the gaffer.
“What he has done has been quite remarkable, getting to a Euros and the World Cup. Now we are going through a transitional period, we have lost some big players and it was always going to be difficult.
“We’ve been in this position before. We had to take it to the Hungary game in the last one to qualify for Euro 2020 so hopefully this can be a similar case.”
Luton captain Tom Lockyer pulled out of the squad on Monday with a thigh injury.
Meanwhile, Eric Ramsay quit his role as Wales assistant manager after the birth of his second child.
The 31-year-old Manchester United coach, who joined the Dragons in March, said: “This has been an extremely difficult decision to make.
“But it is the right one for myself and my family after the recent birth of our second child and taking into consideration the intensity of my role at Manchester United.
“Having discussed everything with my family, Rob and the Association, we came to the conclusion that it was best to depart my role before the upcoming internationals so that the group can fully concentrate on the fixtures.
“I’m extremely thankful to everyone at FA Wales; the experiences throughout the last six months have been amongst the proudest moments of my career to date.
“It was a real pleasure to work with this group of players and I wish everyone nothing but success going forward.”
Sheffield United first team coach Jack Lester has replaced Ramsay.