The Championship side have already bolstered their squad with the return of Benjani, who left Blackburn Rovers in the summer.
Although the 33-year-old penned a one-year deal with Pompey at the weekend, Cotterill is confident that more players will be brought in.
"I'm still hopeful of the loan and a permanent," he told The News. "I might be hopeful of two permanents. That may be before Reading, I'm not sure."
Benjani, who spent two seasons at Portsmouth, made his return to the coastal club after leaving for Manchester City in 2008.
"I've felt we've needed firepower," Cotterill added. "I think we probably still need another striker and maybe another after that.
"Benji brings energy and maybe for a year it might be what we need. He will give everyone a lift - he has done already. He turned down a contract at Blackburn, so I rang him and 24 hours later we were finalising his contract in a car park.
"It is amazing how quickly it happened but we're pleased to get him. Now we have to assess when he goes on the pitch. It might be one where he goes in the deep end and we see what we get from him. I don't know yet."
Portsmouth are scheduled to go head to head with Reading on Tuesday.