Manly have been struck a massive blow with two players ruled out for the rest of the season and star fullback Tom Trbojevic sidelined for a few weeks with an ankle injury.
Tanginoa has suffered MCL and ACL ruptures to his knee, while Sironen has an ACL rupture.
Trbojevic has a medial ankle sprain and is likely to miss two weeks.
Sea Eagles head coach Trent Barrett said it was a disappointing result for Tanginoa and Sironen.
“Both players worked extremely hard in the pre-season and have been very good for us in the first four weeks of the competition,” Barrett said on the club website.
“We all feel for them. Kelepi and Curtis will have the club’s full support.
“It is a big blow to the side but we have plenty of good depth in the forwards, so we will fight on.”