Brendan Rodgers is keen to strengthen his squad further following the arrival of Odsonne Edouard on a permanent deal.
Edouard completed his move to Celtic earlier this month following an encouraging debut campaign on loan from Paris Saint-Germain.
Fans are keen to see the Hoops strengthen their options in defence after January arrivals Marvin Compper and Jack Hendry failed to make an immediate impression, but while Rodgers is looking to add to his squad, he is keen to wait for the right deal.
"The key was to get the likes of Tom (Rogic, who signed a new deal) and Odsonne in," he told CelticTV.
"Like always, there are a few areas that we want to be better in and improve. It's never easy because the team we have is developing very well and I like to develop our own players.
"Everyone goes on about a new centre-half, but I don't think they'd be happy with Billy McNeil playing centre-half!
"We have young players developing very well and they will continue to, but we have to be in the market to bring the best possible players to Celtic but there are two conditions: availability and affordability. We are always on the lookout."
The deal to bring in Edouard was seen as a priority this summer following a loan spell which saw him net 11 times in all competitions, including three in two games against Rangers, particularly with Moussa Dembele continually linked with a move away.