"Jarryd has worked tirelessly here," Tomsula told KNBR Radio.
"What he has been doing in practice has been really good for him and the approach he has taken with it.
"What I mean by that is Jarryd just needed to play football and get the feel of the running game. When Jarryd is working off outside, working in space, that's something he's used to, something he's done. It was more the inside stuff and working off the blocks inside and playing the tighter game between the tackles that he needed to work on.
"Really the only way you work on that is doing it. He has taken the lion's share of our practice squad reps, our look-team reps, inside and working those cuts off the blocks and things.
"His development has been ... He has really been working at it. We'll just see where all that goes. Jarryd is real serious about it. We're all extra happy with what he's doing and the way he's approaching it."
Writing for ESPN, Paul Gutierrez said Hayne's passing over may well have ended his hopes of a recall this season.
"Jarryd Hayne fans waiting in joyful hope for the Australian rugby league star's return to the San Francisco 49ers' active roster were likely dealt a blow to the gut with Tuesday's signing of running back DuJuan Harris," Gutierrez wrote.
"The thinking was that with Shaun Draughn nursing a knee injury suffered in Sunday's 24-14 loss to the Cincinnati Bengals and the Niners extremely thin at running back, they would contemplate promoting Hayne from the practice squad, where he has resided since Nov. 2, two days after the team surprisingly waived him.
"Instead the Niners signed Harris, 27, who has been with the Jacksonville Jaguars, Green Bay Packers, Minnesota Vikings, New Orleans Saints, Seattle Seahawks and Ravens since entering the league as an undrafted free agent out of Troy in 2011."
Veteran 49ers beat writer Matt Maiocco of CSN Bay Area reported the Harris signing as a snub for Hayne.
"The 49ers on Tuesday (US time) bypassed Jarryd Hayne off their own practice squad to sign running back DuJuan Harris off the practice squad of the Baltimore Ravens," Maiocco wrote.
"The 49ers signed Harris and released running back Travaris Cadet. Hayne remains on the 49ers' practice squad, where he has been since the team waived him just prior to the 49ers' Nov. 1 game at St. Louis. Hayne is in his first season of playing American football after leaving behind a successful career in Australia's National Rugby League."
Cam Inman of the San Jose Mercury News also took the signing as a snub for Hayne.
"The 49ers added a running back to their injury-depleted unit Wednesday, and rather than promote Jarryd Hayne from their practice squad, they instead signed DuJuan Harris off the Baltimore Ravens," Inman wrote.
Hayne was dumped just six games into his NFL career after making three fumbles on punt returns and missing blocking assignments. His lack of NFL knowledge has since been criticised by 49ers coaching staff, including special teams coach Thomas McGaughey saying the pre-season star "just didn't work out".
The Niners have signed running backs Cadet, Shaun Draughn, Pierre Thomas and now Harris in preference to giving Hayne another shot in the NFL, while Kendall Gaskins was promoted from the practice squad when the Aussie was waived. Draughn is the only one to impress, though he is now carrying a knee injury.
Maiocco reported Draughn's knee injury may not be as serious as first feared but his availability is uncertain. Draughn being place on injured reserve may be Hayne's only way in, which looks unlikely.
Another running back, Mike Davis, has been cleared to practice after a overcoming hand fracture but won't play the next game against the Detroit Lions - a team Hayne nearly joined. Kendall Gaskins is the other running back on the Niners roster.
Hayne has insisted he will continue to pursue his NFL dream next season rather than return to the NRL. His latest snub may cast some doubt over whether it will be with the 49ers.
