Former Liverpool boss Graeme Souness believes Chelsea will regret selling Nemanja Matic to Manchester United.
Chelsea earned £40m from Matic's departure, which covered the cost of signing Tiemoue Bakayoko from Monaco.
But Souness is not convinced the Blues got the best end of the bargain.
“I have some criticism of the Serb — I would like to see him become more of a box-to-box player, contributing more goals (remember that brilliant strike against Tottenham in the FA Cup semi-final)," Souness wrote in the Sunday Times.
"But he has a great workrate, doesn't give the ball away and was an integral part of two title-winning teams.
"At 29 he is at his peak and I would not have sold him.
"Or, if I did want to move him on, it would not have been to Old Trafford because it only strengthens one of Chelsea's rivals.
"A stronger United makes life harder for Chelsea and I expect Manchester City to do better this season."