It was announced last week that the performance coach of the Mercedes driver would exit her role from inside his inner-circle.
Hamilton insisted there was no breakdown in relationship but Toto Wolff hinted it was his driver’s decision to part ways.
Rosberg said that Cullen’s exit is a potential problem for Hamilton on Sky: “I think that probably makes things even worse.
“Even though the split apparently was amicable, Angela was a real friend.
“It’s with your trainer that most of your time during the race weekend you end up also going to dinner with in a very small, tight group – maybe a family member and a trainer and that’s it.
“For Lewis not to have her I’m sure is gonna be not ideal and not so nice. I think that’s probably another challenge he has to deal with and get used to.”
Cullen was by Hamilton’s side for seven years, dating back to Rosberg’s championship-winning season in 2016 when he was also a Mercedes driver.
Hamilton’s first race without Cullen by his side, the F1 Saudi Arabian Grand Prix, he finished in P5 behind teammate George Russell.
He refused to give details about why she has left her role, but did say: “Angela is a bundle of joy. It’s definitely different, not seeing her during the day and not having her positive energy around.
“But I still have a great team around me.
“She’s here in spirit. She’s been supporting me all weekend through texting. So, yeah.”