Benitez finally scored his first home goal in the Premier League success against the Clarets at St Andrew's on Saturday.
Benitez has been with Blues all season and the Midlands club have the option of signing him permanently from Mexican club Santos Laguna.
But McLeish has still to make any definite decision and hinted that City may want to renegotiate the fee agreed for the Ecuador international last summer.
The former Scotland boss said: "We will cross that bridge regarding Benitez's future when we come to it. I will assess everything in the next couple of weeks.
"We have a deadline of May 25 to decide what we want to do. He has done well for us and we have to consider everything.
"Something could be sorted out before then. The fee is written into the deal but, you never know, loads of deals have been like that before and have become negotiable."
Benitez netted his fourth goal of the campaign - and his first at home - on his 24th birthday to help Birmingham reach the 50-point mark for the season.
They also ensured they have remained unbeaten in front of their own fans since September - a sequence of 15 games.
McLeish said: "We were very keen to get on to 50 points and it was very important to sustain the home record. Not to lose here since September is a marvellous achievement.
"At the beginning of the season we targeted a point a game. Our tally could have been even higher. We have stuttered recently in terms of results but not performances."
McLeish paid tribute to 'keeper Joe Hart, who has been on loan from Manchester City this season.
Hart is now a strong contender to be part of England's World Cup squad after his performances for City.
McLeish said: "People talk about Edwin van der Sar saving 15 points a season for Manchester United. We wanted someone of the same sort of ability to do likewise and Joe has done that."
Burnley boss Brian Laws reiterated his desire to remain at Turf Moor despite their relegation from the Premier League.
He said: "I want to be at the club next season, no question about that.
"We have been preparing for some time for next season, whether we are in the Premier League or the Championship.
"We want to take a leaf out of the book of someone like West Brom who went down, kept most of their squad together and bounced back immediately."
Laws also admitted he would take satisfaction should Burnley qualify for the Europa League because of their outstanding fair play record although it will depend on Fulham winning the competition.
Laws said: "We are Fulham's biggest fans at the moment and it would be great for the club if we could take part in Europe.
"The negative part is we would have to report back earlier but that would take care of pre-season and would be fantastic for the football club."