Dinamo travel to Portugal on the back of a morale-boosting 5-0 victory over Zadar at the Maksimir Stadium knowing they must earn a draw against the Portuguese champions if they are to stand any chance of overhauling the four-point gap to Dynamo Kiev and claim third place in the group.
Porto, who are top of Group A and beat Dinamo 2-0 in Zagreb in their opening pool game on September 18, have already qualified to the knockout stages but will be looking to consolidate their position and earn a potentially better draw.
Porto have also defeated French Ligue 1 giants Paris St Germain and overturned Dynamo Kiev at home before they drew against the Ukrainian opponents on the road in the second part of the double-header.
Dinamo followed up their defeat to the Portuguese champions on matchday one with three more defeats including a 4-0 loss to PSG earlier this month to leave them bottom of the group with no points.
"We have a match in the Champions League against perhaps the strongest team in our group," Kelava told www.gnkdinamo.hr ahead of the match.
"However, although Porto is a great team that has already proved its quality by making sure to qualify for the next round - we're coming into the game on the back of a good result."
The 24-year-old goalkeeper added: "We played really well against Zadar and are filled with self-confidence even though we know it will be difficult because it is an entirely different game - we will not surrender."
Mateo Kovacic, Dinamo's 18-year-old attacking midfielder, is also refusing to write off his side's chances in Portugal.
"Of course, we know it will be difficult and that they are the favourites, but we do not go with a white flag," Kovacic said.
"We go there to play football and try to achieve a better result. With a little luck, who knows what could happen."
Porto, the 2004 Champions League winners, will be without defender Emidio Rafael who has a long-term ankle injury, but manager Vitor Pereira could still make several changes with qualification to the last 16 ensured.
Midfielder Joao Moutinho and striker Jackson Martinez are amongst those who could be rested for the game to give fringe players the chance to make an impact.
Despite this, Porto midfielder Lucho Gonzalez says his side are still focused on earning another win.
He told the club's official website: "Although we have already qualified, we have the objective of finishing the group in the top position. This is an important game coming up."