Bale is returning from an ankle injury which has kept him out since the El Clasico loss to Barcelona in April.
The Welsh winger started as a substitute for Real Madrid against Juventus in his hometown of Cardiff.
Bale has already won two Champions League titles in his four years in the Spanish capital since moving from Tottenham in 2013 and has a knack of scoring in big finals.
"He's scored in many finals, his Copa Del Rey goal against Barcelona was a very, very special goal," McManaman said on BT Sport.
Juventus v Real Madrid combined line-up Sat, June 3, 2017
Click to reveal our Juventus v Real Madrid combined line-up ahead of the Champions League final
Play slideshow Bongarts/Getty Images 1 of 11
GK: Gianluigi Buffon
Steve McManaman thinks Gareth Bale can be a threat for Real Madrid against Juventus from the bench
Gareth Bale's scored in many finals, his Copa Del Rey goal against Barcelona was a very, very special goal
Steve McManaman on Real Madrid star Gareth Bale
"It's unfortunate that this calf injury, I know he's had an operation on his ankle as well, but this calf injury has come at the worst time for him.
"Isco has come in and played really, really well. I think the fact that he is really well, and he looked really sharp in training yesterday on the pitch, he's a great option to have if things are not going well."
Get Quotes on Home Insurance
Rio Ferdinand says there are not many better sights than Gareth Bale in full flow
"I don't think there's many better sights in football than when this guy is in free-flowing motion," he added.
"If it opens up and there's space to be had, he's devastating. He's quick, he's aggressive, he's athletic and he produces goals, glorious goals.
"He's missed 33 out of 59 games and if you want to be part of a great team, you need to be out on the pitch as much as possible."
Bale came on in the final after 77 minutes with Madrid winning 3-1.