Head coach Dean Ryan has made only one change to the starting XV that lost 20-19 to Sale last Friday - recalling Christian Califano to the front row and a reunion with his former club.
There are changes on the bench. Patrice Collazo comes in as front row cover and there is also a recall for lock Will James.
"Agen will play with big intensity, but we have everything we need to win this game," Bortolami told www.gloucesterrugby.co.uk.
"We have only one chance now, and I think it's the right pressure on the team. We have to perform and we have to win.
"Agen try to play open rugby so we have to be careful in defence and try not to give them opportunities to score tries as we did when they played here. They scored four tries from our mistakes.
"Last week at Sale we had two or three chances to score in the second half didn't and lost by one point. We must not throw opportunities away."
Califano will line-up in the front row alongside Welsh international hooker Mefin Davies and Italian tight-head prop Carlos Nieto.
Bortolami and Alex Brown are the locks, while Peter Buxton, Andy Hazell and James Forrester - who this week signed a new contract at Kingsholm - form the back row.
The backline also has a settled feel to it and Rory Lawson and Ryan Lamb will again be the half-backs.
Mike Tindall and Anthony Allen are the centre combination and the back three is also intact and includes James Simpson-Daniel, Iain Balshaw and Olly Morgan.
GLOUCESTER (v Agen, tomorrow): Olly Morgan; James Simpson-Daniel, Mike Tindall, Anthony Allen, Iain Balshaw; Ryan Lamb, Rory Lawson; Christian Califano, Mefin Davies, Carlos Nieto, Marco Bortolami (capt), Alex Brown, Peter Buxton, Andy Hazell, James Forrester. Reps: Olivier Azam, Patrice Collazo, Will James, Jake Boer, Peter Richards, Willie Walker, Mark Foster.