Celtic manager Brendan Rodgers still has work to do in the transfer market this summer.
The Northern Irishman has already secured the permanent signing of Odsonne Edouard while Lewis Morgan has completed his move from St Mirren.
The Hoops squad has been weakened however by the departure of Stuart Armstrong, with the midfielder joining Southampton in a £7million deal earlier this week.
The Scotland international has been a key player during Rodgers’ successive treble-winning seasons, and the former Liverpool boss knows he has a job on his hands to replace him.
“There is no doubt we need to replace, never mind add,” he told Radio Clyde.
“We have lost the likes of Stuart Armstrong, who was a very important player for our squad, and the likes of Patrick Roberts, who was very important for us.
“We need to replace those players and that’s something we hope the club can do over the course of the summer.”
Rodgers is currently in Austria with his squad on a pre-season training tour as Celtic prepare for the upcoming Champions League qualifiers against Alashkert.
He has welcomed back fit-again Jonny Hayes into the squad while youngsters such as Stephen Welsh and Kerr McInroy were given game time in the friendly win over SK Vorwarts Steyr.
And Rodgers suggested that improving his current squad is just as important as being active in the transfer market.
He said: “We have a very stable club, and what I love about our squad is there is a lot of development left still in them.
“You look at the likes of Callum McGregor, where he is now to where he was two years ago and the authority he plays the game with and the confidence, so he will continue to improve with a number of players.”