Ross Barkley went off injured late in the first half of Saturday's 1-0 home win over Newcastle
Chelsea boss Frank Lampard says he is aware of Ajax's "new threats" as he prepares to face last season's Champions League semi-finalists.
Striker Quincy Promes is one new signing that has impressed for the Dutch giants this season following the departure of Frenkie De Jong and Matthijs De Ligt for big money.
Ajax are top of Group H with six points and also lead the Eredivisie.
"We have confidence in ourselves, but it's a tough match," said Lampard.
"I watched them play last year and I know their team has changed slightly. I'm very aware of the new threats they have.
"They've won their two Champions League games convincingly."
Team news
Midfielders Ross Barkley and N'Golo Kante have not travelled for the match in Amsterdam.
Barkley suffered an ankle injury in Saturday's Premier League win over Newcastle while Kante sustained a groin injury while on international duty.
Andreas Christensen and fellow centre-back Antonio Rudiger are also out.
"Ross will hopefully be fit to train by Thursday," said Lampard. "Rudiger trained with us but will be out of contention for the weekend."
Chelsea will assess Kante's injury again before their Premier League trip to Burnley on Saturday (17:30 BST).
Rudiger featured in the squad's last session before leaving for Amsterdam on Tuesday as the Germany defender continues his recovery from a groin problem that has restricted him to just 45 minutes this season.
Christensen is expected to be out for around two weeks after the defender sustained a hamstring injury playing for Denmark.
Chelsea lost 1-0 at home to Valencia in their opening group game but then won at Lille to go into Wednesday's game three points behind Ajax, who made a surprise run to last season's semi-finals.
Best of the stats
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Ajax and Chelsea have not previously met in European competition, with the Blues the ninth different English team Ajax have faced in European competition.
Chelsea are unbeaten in four previous European games with Dutch sides (W2 D2 L0), winning twice against Feyenoord in the 1999-00 Champions League and drawing 0-0 in two knockout games against AFC DWS in the 1968-69 Fairs Cup but went out after losing a coin toss.
Ajax have not won three consecutive Champions League matches since November 2005, beating Thun twice and Sparta Prague under manager Danny Blind.
Since losing 3-0 at Barcelona in March 2018, Chelsea have lost none of their eight away European matches (W6 D2 L0) - their longest unbeaten away run in Europe.
Promes is looking to become the first player to score in his first three Champions League appearances for Ajax, having netted against Lille and Valencia this campaign.
Against Lille, Tammy Abraham became Chelsea's first English scorer in the Champions League since Gary Cahill in November 2015; only three Englishmen have done so in consecutive games for the club - Frank Lampard (five times), John Terry (three times) and Dennis Wise (twice).
Source: bbc.com