An entry list released by the Japanese series on Thursday has Sasahara listed in the cockpit of the #3 Kondo car, with Yamashita still recovering from injuries he sustained in a SUPER GT testing crash in January.
Yamashita is aiming to be fit in time for the opening round of the season at Fuji Speedway in April.
Sasahara, a winner of two races last year, was left without a regular drive in Super Formula after switching from the Honda camp to Toyota last season.
He participated in the second day of last December's post-season test at Suzuka with the TOM'S team, with which he will race in SUPER GT this year, but ultimately lost out on a race seat to Giuliano Alesi.
Sasahara does however already have experience of the upgraded SF23 chassis that Super Formula will use this year, as he took part in a wet test at Motegi last month in his first assignment as the development driver for the Toyota car.
Elsewhere on the Suzuka test entry list, Turkish driver Cem Bolukbasi has been named as one of the reborn TGM Grand Prix outfit's two drivers, with the other seat still listed as 'TBN'.
Bolukbasi drove for the Servus Japan-run TGM squad at Suzuka in December, and is expected to be confirmed as a full-season driver for the team imminently.
Toshiki Oyu, who has left Nakajima Racing after three seasons, is expected to take up the other seat.
One other point of interest on the entry list is that Tomoki Nojiri's #1 car is listed as the 'Red Bull Motul Mugen SF23'.
This suggests that the defending champion will be running in a Red Bull-liveried car this year, along with new team-mate Liam Lawson.
The Team Impul machines of Yuhi Sekiguchi and Ryo Hirakawa are also both listed as 'Itochu Enex Team Impul SF23', hinting at a possible return to the team's old white-and-blue colours.
The two-day test at Suzuka begins on Monday, and represents the only on-track running ahead of the opening races at Fuji on April 8-9.
Suzuka test entry list (March 6-7):
| Team/Engine | No. | Driver |
|---|---|---|
| Mugen/Honda | 1 |
 Tomoki Nojiri
|
| 15 |  Liam Lawson |
|
| Kondo Racing/Toyota | 3 | Ukyo Sasahara |
| 4 |
Kazuto Kotaka |
|
| Dandelion Racing/Honda | 5 |
Tadasuke Makino |
| 6 |
|
|
| KCMG/Toyota | 7 |
|
| 18 |
|
|
| ThreeBond Racing/Honda | 12 |
|
| Rookie Racing/Toyota | 14 |
|
| Impul/Toyota | 19 |
|
| 20 |
|
|
| TOM'S/Toyota | 36 |
|
| 37 |
|
|
| Inging/Toyota | 38 |
|
| 39 |
|
|
| B-Max Racing/Honda | 50 |
|
| 51 |
|
|
| TGM Grand Prix/Honda | 53 |
TBA |
| 55 |
|
|
| Nakajima Racing/Honda | 64 |
|
| 65 |
|
Raoul Hyman
Cem Bolukbasi
