The Lions top Pool 3 with 14 points, but Ella knows a slip-up at home to the Cardiff Blues this weekend or a loss on the daunting trip to Biarritz Olympique in Round 6, could seriously damage their chances of making it through to the Heineken Cup quarter-finals for the third year in a row.
'We'll be favourites at home against the Blues, but the way I see it, it doesn't mean anything,' said the former Australian international. 'The way the competition has panned out, we've got to win - it doesn't matter if we're red-hot favourites or underdogs.'
Ella said he was rapt with his side's 22-15 win at Sale on Sunday, but the victory came at a price.
'We lost Eric Miller and Victor Costello during the game, and the guy who replaced Victor - Des Dillon - also has a shoulder injury, so it's not looking too good in the back row.
'Miller has a shoulder injury which we're keeping an eye on, but Victor's knee should be okay for the Blues game.
'It was a pretty tough game and I thought our defence was outstanding. There are a couple of concerns over what we do with the quality ball we manage to get, and we are turning over a lot of ball in the line-out.
"In the end it was our defence that won us the game. We talked a fair bit during the week about defensive alignement and communication and I thought we were outstanding in those areas."
Ella also paid tribute to skipper Reggie Corrigan, who won the Heineken man of the match award in the hard-fought victory at Edgeley Park.
'I thought he was outstanding - he did a huge amount of work around the paddock, and his leadership was terrific. Gordon D'Arcy also had a superb game.'
And Ella said he wasn't taking too much heart from Leinster's 24-19 win over the Blues at the Arms Park in Round 2 either.
'We had pretty atrocious conditions that day. They didn't favour either side, but made things difficult," he said. 'The Blues are a very physical, very strong side, with a mobile back row which we're concerned about. Their outside backs are slick as well, so they're dangerous out there.
"We were delighted with Cardiff winning their first game and I am sure that will spur them on. They will want to come to Dublin and prove that victory over Biarritz was no fluke. We are expecting a very physical challenge from them on Friday night. We have already had two bruising games against them and it is a game that will be won and lost in the forwards."
Ella is expecting a big crowd to roar his side on at Lansdowne Road. "We had 14,200 at the last game at Lansdowne Road and the win over Sale should see an increase - possibly to over 20,000 - which will be a big boost for the boys.'