Rafael da Silva told Ole Gunnar Solskjaer to keep fighting as Manchester United manager.
United recorded a 4-1 win over Istanbul Basaksehir in the Champions League on Tuesday evening - a result that keeps them top of Group H.
It was a match notable for United cult hero Rafael's return to Old Trafford five years after he departed for French club Lyon.
The Brazilian now plays for Basaksehir after moving from France on a free transfer in the summer, but he is still keeping tabs on United.
Rafael posted a message on Twitter post-match, telling Solskjaer and United to keep fighting.
He said: "Just hope the best for you and Manchester United, keep fighting my friend like you are doing. All the best Man United, thank you for the warm welcome before and after the game. Love you all."
The right-back echoed these words in a post-match interview with club media, revealing he had held a conversation with Solskjaer after the game.
He said: "I just spoke with Ole, I hope United get all the wins they need. Ole's a good manager, a good guy and I hope he does very well for this club."
Rafael's former teammate Rio Ferdinand paid tribute to the Brazilian and said United made a mistake to sell him to Lyon in 2015.
"Great kid, he's a really warm kid and a really great family as well," Ferdinand told BT Sport. "He was a really dogged player, he wasn't a typical Brazilian of flair that you'd expect to see, he was someone that was really diligent in his work ethic.
"Aggressive, everything you want in a modern-day right-back. Up and down, energetic, can deliver the ball as well.
"I thought he was unfortunate to be shipped out of United when he was. He's had a few injuries of late but he's someone who has carved out a really good career for himself.
"That was never in doubt when he came as his attitude was spot on."
