The Gers boss has completed deals for Kenny Miller and Darren McGregor so far during the close season but has missed out on Gavin Gunning and Shaun Hutchinson after they joined Birmingham and Fulham.
Defensive duo Ross Perry and Chris Hegarty were told they were surplus to requirements earlier this summer while Emilson Cribari's contract has expired.
And McCoist is keen to delve into the transfer market once again ahead of the Championship kick-off.
He said: "We definitely need options. We have lost a couple of defenders in the close season.
"It is safe and fair to say that we are looking to strengthen in that area.
"Having said that, our two centre-backs last year (Lee McCulloch and Bilel Mohsni) scored 25, 30 goals between them and, along with the rest of the defence and rest of the lads, kept a very, very good number of clean sheets.
"We have weakened that defensive area in numbers in the close season and we certainly need to strengthen it."
The capture of McGregor last week was McCoist's second bit of business of the summer as the stopper completed his switch from St Mirren.
He has suffered two cruciate knee ligament injuries in recent years, but McCoist has no fears over the fitness of the former Cowdenbeath player.
He said: "I went to watch St Mirren a good number of times last year and we felt that Darren was certainly one of their more experienced and consistent performers.
"We have watched him for a couple of years now and it was important coming back from the injuries that he showed no signs of it.
"The fact that he played 40-odd games would indicate that he is well over it.
"These are the reasons we think he will be a great addition to the squad."
Rangers will return to pre-season action in a couple of weeks as the countdown continues to the new Championship campaign.
The Light Blues will round off their summer schedule against English outfit Derby County and McCoist reckons it will be the ideal test for his side ahead of a tough campaign.
"Coming to the end of our pre-season, it gives you a good idea of just how far you have come," he told RangersTV.
"It is right at the end of our pre-season and Derby will be looking at it, hopefully, as one of their tougher fixtures as well.
"These games are vital, they really are, in terms of preparation for the season ahead.
"Most managers and coaches will agree that the result and level of performance isn't of the greatest importance.
"It is the levels of fitness and how ready you are to peak for the start of the season that is most important."