Mourinho rose to prominence at Porto, guiding the Portuguese side to the Champions League title in 2004 before moving to Stamford Bridge for his first spell.
The Blues lost 2-1 in Porto in the second round of matches, but a win would see them advance at their visitors' expense and at the top of Group G - assuming Dynamo Kiev win at home to Maccabi Tel Aviv, who have one goal and zero points from five games.
The group was blown wide open by Dynamo's win at Estadio do Dragao in the last round of matches, when Chelsea won 4-0 in Israel to go top of the standings on 10 points.
Porto also have 10 and Dynamo eight, meaning all three teams can advance, or miss out.
A draw would be enough for Chelsea to go through, but Porto would be eliminated on goal difference in matches between the three teams and fall into the Europa League if Dynamo win and the Stamford Bridge contest is even.
Defeat, third place and the Europa League is not something Mourinho wishes to contemplate, after often deriding predecessor Rafael Benitez's success in the second-tier competition.
Chelsea in 2013, under interim boss Benitez, won the Europa League after becoming the first reigning European champions to exit the Champions League at the group stage in defence of their title.
Mourinho's men have won both their home games so far in the tournament, which has offered some respite from a torrid domestic campaign which has only recently showed signs of a revival.
Mourinho says Porto can prioritise their Champions League tie, due to the inferior opposition in the Primeira Liga, but Chelsea cannot
Porto play Pacos de Ferreira on Saturday.
"When I was coaching Porto, when I was in Portugal, I could think about next because normally in Portugal we knew that we are going to win the match," Mourinho said.
"The percentage of victories is so high that you can think about other competitions
In England that's not possible.
"In England our situation is so bad we have just to focus on the Premier League."
Source : PA
Source: PA