Chelsea boss Jose Mourinho has explained shaking up his midfield last month.
"They are young players, hungry for success," he told Chelsea Magazine. "Nemanja is 25 and Mohamed is 21, so I think you can see we are trying to build a team for the future.
"Matic has grown as a player during his time in Portugal and he has come back to this club as a fantastic all-round midfielder.
"As for Salah - he is a young, enthusiastic player with great pace and we have seen that he can score goals and create chances for his team-mates."
Mourinho also hinted that Mata and De Bruyne's work-rate was a factor in their sales.
"We also looked at how hard he [Salah] works for the team and decided that he would be a good player for Chelsea and for this league," Mourinho added.
"He has the character and the ambition to make this move and to be a successful player for us.
"I think both of them will become very important players here and they will help us to achieve our ambitions this season and beyond, as part of a strong squad.