The absence of Edinson Cavani in Tuesday's 1-1 home draw against Anderlecht suggested that Paris St Germain may need more striker reinforcements if they are to be real contenders in the Champions League.
The Uruguay striker was ruled out with a thigh injury and Zlatan Ibrahimovic was required to salvage a point for the weary Ligue 1 champions, who extended their unbeaten streak in all competitions to 32 games.
"It's a good wake-up call," coach Laurent Blanc told reporters.
Big-spending PSG are highly likely to qualify for the last 16 and a home draw against Olympiakos Piraeus in three weeks would see them through as Group C winners.
They have 10 points from four games and lead Olympiakos by three points with Benfica in third place on four. Anderlecht are bottom on one point.
But with Cavani in the starting line up on Tuesday, PSG might already be through to the knockout stage.
His absence was felt as Lucas, whose pace can be devastating, still lacks inspiration and Ezequiel Lavezzi has lost his scoring touch.
"He (Cavani) is a player who scored goals. We have players who do that, Zlatan and Edi, but tonight he was not there," said Blanc.
"He brings a lot of depth. He has an interesting role, especially against teams who regroup. All great forwards in Europe score goals. Others must improve in that area," he added in a veiled reference to Lavezzi and Lucas.
PSG lacked their usual sharpness up front and sometimes looked passive in the midfield, allowing their opponents to build up nicely as it was the case in the 68th minute when Demy de Zeeuw scored from Sacha Kljestan's back pass.
"The players are very tired," Blanc admitted, adding he did not think his team failed to show character.
PSG, however, are still unbeaten this season and Ibrahimovic netted his seventh Champions League goal of the season, two weeks after scoring four in a 5-0 hammering of Anderlecht.
Cavani has already scored 11 goals from 15 matches in all competitions, although he has been mostly fielded on the right flank as Blanc favours a 4-3-3 line-up.
Between them, Cavani and Ibrahimovic have scored 23 goals, while Lucas only found the back of the net twice and Lavezzi once this season.
Blanc, however, admitted that his team were in a good position to qualify after hitting a minor speed bump on Tuesday.
"The next game will be decisive. We will want to win it. But we are well placed," he said.
"(The Anderlecht game) showed that we don't just have to step onto the pitch to win," Blanc reminded.
His players were optimistic they can get it right against the Greeks.
"I'm confident that we will clinch qualification in the next game," said midfielder Blaise Matuidi.