Centre Collis has been a hit since joining from Cronulla Sharks at the end of 2011, scoring 26 tries in 54 games during his first three seasons at the club.
This year, he has scored just twice after injuries limited him to only another 11 appearances but it is “family reasons” why he asked for an immediate release from his contract with Super League’s bottom side.
Collis, 29, has not got a club in the NRL but Smith, the Australian coach who takes charge of Trinity for the first time against Salford Red Devils on Sunday, said: “I believe he has some family matters that have been pressing for quite some time.
“He’s hung on and hung on and eventually just needed to go.
“It’s not personal. Not with me. To be honest, I didn’t see him here.
“He was getting ready to go home when I arrived. It’s not to do with me or the club but whatever it is back home.”
Fellow Australian Sammut, meanwhile, could move to Whitehaven, Leigh or Workington in the coming days.
The 28-year-old has been on the periphery for some time at Belle Vue and he is set to follow Collis and Lopini Paea, the prop who headed back to the NRL last week.
On recruiting fresh blood for their battle to end a 15-match losing run in Super League and aid their fight against relegation, Smith said: “We’d definitely like to if we can.
“We’ve got some space now - finance wise and quota wise - and our phones have been ringing the last few days so without getting everybody too excited something will happen in the next week or two.”
But they will be down to the bare bones for his first game in charge against opponents who have lost eight successive league games themselves.
“We’ve no Ali Lauitiiti, Craig Hall and Richie Owen who we lost last weekend,” said Smith.
“Matty Ashurst’s due back shortly, there’s a bit of question mark on Reece Lyne and Scott Anderson’s still suffering from that bad concussion he had.
“We’ve got a squad of 19 for Sunday, so can afford for a couple more to drop out and we’ve still got 17 but I hope we don’t.”