Speaking ahead of his first European appearance since last January, Danielli said: "Playing for Ulster at Ravenhill is very special and when Trimby (Andrew Trimble) pulled out last week, it gave me a chance to start on the bench and then Timoci went off.
"With the amount of good players in our squad, when you get a chance you have to take it. Thankfully during the game a few holes opened up."
Danielli was sprung for the bench and ran in two tries in last weekend's 53-13 Magners League win over Connacht.
Also back to full fitness, Trimble will return to the starting line-up against the Scarlets. He has been pencilled in on the left wing in place of Mark McCrea who drops to the bench.
The province's forward selection remains the same from the Connacht game.
Looking forward to his side's European return, Matt Williams said: "We are still in the Heineken Cup, we have to win all four (remaining games).
"We are playing every team in the pool and if any one of them slips up, which there is a strong chance of with Stade at 'Quins, and we win our next two games, we are in it.
"But that will mean nothing if we don't win at home. But even if we were out of it, which we are not, the attitude wouldn't change. We would still go flat out at Ravenhill.
"We have worked too bloody hard and been through too much pain and come together so far to come out at Ravenhill and just say, 'it doesn't matter'. That's just not going to happen."
This is a must-win game for Ulster who lie fourth in the Pool 4 table, with pace setters Harlequins and Stade Francais nine points ahead of them.
But Williams' charges have been boosted by recent wins over Munster and Connacht in the Magners League and Portugal in a friendly.
That good run of form together with the usual vocal backing of the Ravenhill faithful will give the Rory Best-captained side plenty of confidence as they look to kickstart their European challenge.
Best said: "It is an old saying and a bit of a cliche but it is true - our supporters really are the 16th man and they really do help us.
"It says a lot about our supporters that they have stuck by us week in, week out over the last year when things haven't been going so well, it really means a lot to us that they do stick by us.
"It drives us on and we feel now that we can give them some good rugby to watch, we are improving and we want them to see that, we want to give them more to cheer about and to support.
"I know there isn't much spare cash about at the minute and people are finding it tough, so I just want to encourage our supporters to come along to Ravenhill to watch Ulster play and I hope that they will go home happy and feeling proud of their province and their team."
Match tickets are available via www.ulsterrugby.com, the Ravenhill Ticket Line (tel: 02890 493 222, Option 2) or through the Ravenhill Ticket Office (Monday-Friday, 9am-5pm).
ULSTER (v Scarlets): Bryn Cunningham; Simon Danielli, Darren Cave, Paddy Wallace, Andrew Trimble; Ian Humphreys, Cillian Willis; Justin Fitzpatrick, Rory Best (capt), BJ Botha, Ed O'Donoghue, Ryan Caldwell, Stephen Ferris, David Pollock, Robbie Diack.
Replacements: Nigel Brady, Tom Court, Matt McCullough, Kieron Dawson, Isaac Boss, Paul Steinmetz, Mark McCrea.