Tottenham host Slovenians Mura in the Europa Conference League on Thursday looking for a confidence boost after a worrying slump in form, while their former manager Jose Mourinho takes his free-scoring Roma side to Zorya Luhansk.
Spurs kicked off the Premier League season under Nuno Espirito Santo with three straight 1-0 wins, but have since suffered three successive defeats, shipping nine goals in the process.
Their tame defeats by London rivals Crystal Palace, Chelsea and Arsenal have raised questions about new manager Nuno.
Harry Kane is yet to score in five league games since failing to force through a close-season move to Manchester City.
"The performance was not good. The game plan was not good. The decisions were not good," former Wolves boss Nuno admitted after the chastening 3-1 derby loss to Arsenal on Sunday.
Spurs are also in need of points in the inaugural Conference League after opening the group stage with a 2-2 draw at Rennes.
Anything other than victory against Mura, who sit fifth in the Slovenian top flight, would see Nuno and his side come under more scrutiny before this weekend's game against Aston Villa.
Spurs, without a trophy since 2008, parted ways with Mourinho shortly before last season's League Cup final loss to Manchester City.
But the Portuguese has enjoyed a strong start to life with Roma, despite suffering a 3-2 loss to Lazio in last week's derby clash.
Often criticised by Spurs fans for his perceived negative style of play, Mourinho has seen his Roma team score 24 goals in only nine matches this term.
He will be looking for a reaction from his side against Luhansk, though, after railing against refereeing decisions in the Lazio loss.
"The referee and VAR weren't up to the standards of a match of this level," he said.
Mourinho, a two-time Champions League-winning coach, now finds himself managing in the far less glamorous third-tier Conference League.
But Roma sent out a statement of intent last time out in Europe as a strong side thumped CSKA Sofia 5-1.
Scottish giants Celtic have endured a difficult campaign so far despite some sparkling home displays under Ange Postecoglou.
They welcome Bayern Leverkusen to Parkhead after slipping to a 4-3 loss to Real Betis in their Europa League group-stage opener.
A strong start to the season at home has provided respite, but Celtic were held by Dundee United at the weekend in Glasgow to fall six points behind reigning Scottish Premiership champions Rangers.
A win over Bundesliga side Leverkusen would lift some of the gloom over the Hoops, after they were booed off by their own fans on Sunday.
Steven Gerrard's Rangers need a positive result at Sparta Prague to boost their hopes of reaching the knockout stage for the third consecutive season after losing to Lyon.
Lyon play Brondby at the Groupama Stadium in the other Group A encounter.
Elsewhere, in-form West Ham host Rapid Vienna and Leicester visit Legia Warsaw.
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