Cronulla will send prop Ava Seumanufagai for scans after the Sharks strongman left the field early in the 28-22 win over Manly on Saturday night.
A second forward - Cooma product Jack Williams - is also suffering a leg injury, but the severity is yet to be determined.
"Hopefully they both have just corks. One of the main things about trials is that you want to come through them unscathed," coach John Morris said.
"I'm hoping Ava isn't a medial [ligament] so we've just got to get that scanned."
Overall, Morris was pleased with the hit-out despite the two clubs carrying different approaches into the match.
While Manly had virtually their full starting forward pack and only hooker Api Korosiau missing from their spine, Cronulla was a long way from the 17 expected to be named for the round one match against the Knights.
Newest Sharks recruit Shaun Johnson wasn't there and neither were a host of other representative players such as Matt Moylan, Paul Gallen, Andrew Fifita, Jayson Bukuya, Matt Prior or Aaron Woods. Josh Dugan is still recovering from off-season surgery.
Match Highlights: Sea Eagles v Sharks
"The side that Manly rolled out were virtually at full strength and we were a long way from it," Morris said. "But [the] conditions made it a pretty dim sort of affair."
Several heavy showers and strongly southerly winds buffeted the players and sections of the meagre crowd that turned up at Shark Park.
"I was a little disappointed with our first half," Morris said of the 18-12 score at the break.
"But they hung in well considering we only had 30 per cent of the ball. There's a lot we can improve on but there were some good signs there."
Morris was heartened to see Sione Katoa score one of the Sharks five tries after he failed to notch a four-pointer in the 20 games he played in his rookie season.
"I thought Kyle Flanagan had some nice touches and Blayke Brailey was slick out of dummy-half," he said.
That will put his brother and starting No.9 for the past two seasons, Jayden Brailey, under some pressure.
Morris happy with Sharks' first hit out
Flanagan, whose father and former Sharks coach Shane Flanagan watched in the stands, played five-eighth for the first half against Manly and then reverted to No.7 for the first 20 minutes of the second.
With Johnson expected to be Morris' starting No.6 for the opening of the new Telstra Premiership season, alongside regular No.7 Chad Townsend, it gives Morris great flexibility that Flanagan can cover both positions.
"I've made it pretty clear to Kyle that it's up to him with his performances and keep on putting his best foot forward at training, then he’ll be driving Chad and Shaun all the way."