Whilst its successor, the W14, is a considerable improvement and the porpoising has been eradicated to a bare minimum, Russell does not believe the car is yet good enough to challenge Red Bull for victory next weekend.
The British driver's remarks were an echo of the comments aired during the team's recent launch when caution appeared to be the watchword.
“We definitely believe, eventually, we will have a car capable of getting in the fight,” said Russell at the midway point of the three-day test at the Bahrain International Circuit.
“Whether we're going to have that next weekend in Bahrain may be a bit of a stretch.”
Verstappen and Red Bull looking “very strong” – Russell
Offering his assessment of the RB19, Russell added: “They look very strong, very stable. The car is looking really strong and obviously, Max is performing really well.
“So I think realistically, it (a victory) will be a stretch for next week, but there's no reason why, eventually, we can't get there at some point this year.
“We've always seen the strength of Mercedes and their development rates. So definitely, the belief is there.”
As to where he feels the W14 is arguably lacking at present, he said: “The entry phase (to the corner) has been improved.
“It's no secret when you're watching the onboards and the videos that we are struggling a little bit with the balance, struggling a lot in the mid-corner.
“But I think it's a balance that is probably easier to solve than we had last year. Even though it's still a limitation, I think it's a good problem to have.”
During the second session on day two, Russell stopped on track, with his car stuck in fourth gear, resulting in the second red flag of the test related to car trouble.