Matic, who had two spells at Stamford Bridge, has reunited with Jose Mourinho at United.
Chelsea manager Antonio Conte says the sale of Nemanja Matic to Manchester United is a “great loss” to his Blues.
The Italian is convinced the £40m Manchester United paid to sign the Serbian played a part in his move to Old Trafford.
"Matic knows very well what I think about him," Conte, speaking at the Premier League Launch, told Sky Sports.
“The importance for me about this player, who is a really good player, a top player, very important for our team, but sometimes you must accept this crazy transfer market.
"And sometimes you must accept different decisions. But I repeat he is a great loss for us."