Chelsea have been handed a boost ahead of their clash against AC Milan in the Champions League in midweek.
Odsonne Edouard put the Eagles ahead before Aubameyang levelled in the first half with a first time finish from a Thiago Silva header.
Gallagher scored in the final minutes of the match, scoring a fantastic long shot to snatch the three points.
AC Milan, on the other hand, beat Empoli 3-1 in Serie A action.
The Italians sit top of the Champions League group, with Chelsea at the bottom.
A loss to Dinamo Zagreb and draw to FC Salzburg has seen the Blues rock bottom of the group, knowing that they must get a positive result against AC Milan.
Chelsea have been handed a boost ahead of the clash, as Italian media have reported.
The situation in Milan is described as a 'crisis', as Football Italia report that AC Milan could have just 14-15 senior outfield players for the clash.
Davide Calabria was stretchered off against Empoli with a suspected hamstring strain which could see him out until the new year.
Furthermore, Simon Kjaer has an issue with his thigh and Alexis Saelemaekers has a sprained knee.
This comes as the Italians are already missing Mike Maignan, the first choice goalkeeper, Junior Messias, Theo Hernandez, Divock Origi, Zlatan Ibrahimovic and Alessandro Florenzi.
Origi may be available for the clash at Stamford Bridge as Messias could also be rushed back.
In the Champions League, Ciprian Tatarusanu, Aster Vranckz, Malick Thiaw, Yacine Adli and Chelsea loanee Tiemoue Bakayoko were all excluded from the squad due to a lack of homegrown players.
This means that AC Milan could face Chelsea with just 14-15 senior outfield players available in the week.
Chelsea know that they must look to beat the Serie A side if they are to stand a chance of qualifying with four matches left in the group.
After the home clash, Chelsea go to the San Siro as they look to qualify for the next round.
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