In what was a repeat of last season's final, Sale's 20-10 victory on Saturday's last day of the regular campaign came despite Tuilagi, celebrating his 33rd birthday, being forced off with a hamstring injury after 17 minutes.
There are now fears the powerhouse England centre's season could be at end and that he will miss the semi-final against Bath on June 1st and a possible Twickenham final before his move to French club Bayonne.
But Sale supremo Alex Sanderson, trying to remain optimistic about Tuilagi's prospects, said: "He has definitely pulled his hamstring, we just don't know how badly.
"He is a quick healer, we know that and we have got two weeks to put 'Humpty Dumpty' back together again and we will give him as long as we can."
Saracens' defeat condemned them to a last-four clash away to Northampton on May 31st after both clubs kicked off on Saturday having already secured play-off berths.
This result also meant Saracens star Owen Farrell had played his last home game for the London club ahead of the former England captain's post-season move to Paris-based Racing 92.
Saracens suffered a setback before kick-off when Scotland wing Sean Maitland, who announced on Friday he would be retiring at the end of the season, pulled out with a freak warm-up injury.
Tries from Tom Roebuck and Rob Du Preez saw Sale establish a 20-3 lead with 30 minutes left.
Saracens threatened a fightback when Marco Riccioni went over to make it a 10-point game.
But Sale held firm as they enjoyed a first away league win over Saracens since September 2005.
Bath secured their play-off place by scoring six tries in a 43-12 rout of Northampton.
Bristol overwhelmed Harlequins 58-23 and Leicester defeated Exeter 40-22 but results elsewhere denied the Bears and the Tigers a play-off spot.
No wins for Newcastle
Newcastle ended the Premiership season without a single win after a 54-14 loss at home to Gloucester.
Defeat meant Newcastle followed Rotherham (2003/04) and London Welsh (2014/15) in failing to post a solitary league win in a season.
Newcastle's owners deliberately reduced their spending on players after three other Premiership clubs - Worcester, Wasps and London Irish - all went bust last season.
Given there was no realistic prospect of relegation they relied on a young and inexperienced squad, with the club prepared to suffer short-term pain in the hope of avoiding the extinct trio's example.
For Gloucester, who suffered a humiliating 90-0 defeat by Northampton last time out, this was a morale-boosting win ahead of next week's European Challenge Cup final against South Africa's Sharks.
"I was concerned about the scoreline last week and in the close season, I will need to review that in some detail as to how we conceded so many points," said Gloucester director of rugby George Skivington.
"It was a totally different team and I thought we completed our league season with a bang."
Defeat was a familiar story for Newcastle, with consultant boss Steve Diamond saying: "Realistically it's the tale of our season as we have regularly failed to take our chances and it has certainly cost us."
