Steven Davis says Rangers go into the first Old Firm derby of the season still short of their best form but determined to find it against Celtic.

The 36-year-old midfielder is a veteran of games between the Glasgow rivals, with Rangers unbeaten in the last six.

But a Rangers side struck by Covid-19 struggled to beat Alashkert in Thursday's Europa League play-off.

"Things haven't been as smooth as we would have liked and we certainly know we can perform better," Davis said.

"The most important thing is we are in that hat for the group stage four seasons on the bounce now and it's a great achievement."

Their 0-0 draw in Armenia, on the back of a 1-0 first leg win, means Rangers are now unbeaten in four games after a worrying three-game losing streak, while Celtic's six-game winning run was ended as they progressed to the group stage despite a 2-1 defeat away to AZ Alkmaar.

"You can't go on previous results," Davis said of Sunday's derby at Ibrox. "We just know we have to be at our best.

"If we perform at our highest level, we'll give ourselves a good opportunity to get the result we want."

Davis reckons that the reigning Scottish champions can still field "a strong, quality team" despite their Covid cases, suspensions and injuries and that, once they find their form, "we'll be a real force".

Rangers manager Steven Gerrard was absent in Armenia and again from Friday's media conference, at which assistant Gary McAllister pointed out that they would have a larger squad from which to pick after Thursday's substitutes' bench was dominated by teenagers.

Juninho Bacuna, their summer midfield signing from Huddersfield Town, winger Brandon Barker and centre-half Nikola Katic, who has returned from long-term injury, had not been named in Rangers' European squad and will be available on Sunday.

Meanwhile, striker Kemar Roofe and midfielder John Lundstram return from European suspension.

Goalkeepers Allan McGregor and Jon McLaughlin, captain James Tavernier and fellow full-back Calvin Bassey, plus wingers Scott Wright and Ryan Kent, also did not travel to Yerevan.

McAllister said: "We adapt day by day to see who is available and who is not. That's all we can do.

"It has been a tough three or four days. If we all can come together, we can hopefully get a result."