Lazio coach Stefano Pioli was left hopeful over Lucas Biglia's injury as he looked ahead to Wednesday's Champions League clash against Bayer Leverkusen.
Biglia, a reported transfer target for Manchester United, came off in the 52nd minute of Lazio's 2-1 Serie A win over Bologna on Saturday.
The club confirmed Biglia, who opened the scoring in the victory, had suffered a calf injury that would require further tests to determine its severity.
Pioli was hopeful as Lazio prepare to head to Germany for the play-off having won the first leg 1-0.
"Our next game is hugely important as it'll tell us which European competition we will take part in," he told Sky Sport Italia.
"The team is competitive. Unfortunately, we had a few too many injuries and hope Lucas Biglia doesn't have anything serious."
Leverkusen will also take winning form into the second leg after overcoming Hannover 1-0 in the Bundesliga on Saturday.
Meanwhile, Monaco welcome Valencia to the Stade Louis II with the La Liga outfit holding a 3-1 advantage.
Both failed to win league matches on Saturday as Monaco were held at Toulouse and Valencia drew at Rayo Vallecano.
Manchester United are well-placed to reach the group stages as they head to Club Brugge also leading 3-1.
Marouane Fellaini's late goal at Old Trafford has given them a two-goal buffer, but Louis van Gaal's men are struggling for goals – having scored just twice in three league games this season.
There remains greater uncertainty about all of the other ties.
Leigh Griffiths' brace helped Celtic beat Malmo, but the Swedish side host the second leg after the 3-2 loss in Scotland.
Shakhtar Donetsk will fancy their chances of reaching the group stages, leading Rapid Vienna 1-0 ahead of the second leg in Ukraine.
Basel visit Israel's Maccabi Tel Aviv after a 2-2 draw in Switzerland, while Astana head to APOEL holding a 1-0 lead.
CSKA Moscow are trailing 2-1 ahead of hosting Sporting Lisbon and BATE take a 1-0 lead to Partizan Belgrade.
Croatian club Dinamo Zagreb hold the upper-hand in their tie against Skenderbeu Korce, having won the first leg 2-1 in Albania.