The arrivals of Francisco Sandaza, Kevin Kyle and Emilson Cribari brought his new recruits to five so far, having already signed Dean Shiels and Ian Black.
But, with a 12-month transfer embargo set to come into effect on September 1, McCoist still has concerns over numbers as Rangers prepare for life in the Irn-Bru Third Division this term.
Speaking after Tuesday night's 4-0 win over East Fife in the Scottish Communities League Cup, the manager said: "We are in a transitional period as a club and as a team.
"You don't lose 23 players in six months and expect to be anything other than that.
"We've brought five in. I keep hearing people saying we're not going to lose a game but the fact is we've got to earn the right to win games.
"We'll get a lot of tough games and I think we still need to bring in players. The maths would tell you that, we definitely need players in, especially with the embargo in place after September.
"We'll certainly be looking to strengthen the squad."
Former Hearts striker Craig Beattie had been training with Rangers and remains a target for now, with McCoist set to hold talks with chief executive Charles Green.
He added: "We are hopefully going to have a chat about that later tonight and tomorrow morning.
"We will see if we can push that one forward but there is nothing as yet that I can tell you in terms of signing.
"Craig is certainly one player we have been looking at and there are a good number on the radar as well."
Shiels marked his debut with a goal, while Lee McCulloch grabbed a double and Lee Wallace was also on the scoresheet as Rangers cruised into the second round.
The match was the first at Ibrox since the club was consigned to liquidation in the summer and voted into Division Three, and more than 38,000 fans packed into the stadium.
McCoist said: "I've got to say the support was absolutely amazing. I genuinely couldn't believe it.
"I was hopeful we would reach somewhere in the region of 30,000. Out of all this madness in the last 10 months, our fans have been a major plus.
"It's been phenomenal and the players and staff are extremely grateful for it. Tonight was just another exhibition of what they have been doing."
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