Nemanja Matic said it was "strange" being frozen out at Chelsea after making his debut for Manchester United on Wednesday.
The Serbia international played the first half of United's 2-1 victory over Sampdoria as Jose Mourinho's side completed their pre-season schedule.
It was Matic's first match since the FA Cup Final after he was ordered to stay in London as his then Chelsea team-mates embarked on a tour of the Far East in July.
The 29-year-old trained alone at Chelsea, but says he has received a warm welcome following his £40million move to Manchester United on Monday.
He told the club's in-house TV channel: "It was strange [not playing in pre-season] because the team has played and had a good pre-season but, as you know, I trained alone in London."
Matic impressed as goals from Henrikh Mkhitaryan and Juan Mata helped United prepare for the new season in the best possible fashion.
Mourinho's men will now play in the Uefa Super Cup against Champions League holders Real Madrid on Tuesday before their Premier League opener against West Ham on August 12.
"I must say thanks to the guys," Matic added. "They've helped me to already become part of the team and they are all nice guys. I think the staff have also helped me a lot, and I say thanks to them because they've accepted me very well already."
