Martin O'Neill rages with Celtic fans after their protest vs Stuttgart

Celtic hosted Bundesliga side Stuttgart last night in the UEFA Europa League, with the two sides playing at Celtic Park in their play-off first leg.

Just 15 seconds into the game in Scotland, Celtic fans threw balls onto the pitch in protest against their owners and the club's hierarchy. It took around four minutes to clear the pitch and resume play after toy balls were chucked from the stands onto the playing field.

The Bhoys went on to suffer a difficult 4-1 defeat, putting them on the verge of being knocked out of the Europa League unless they can produce a spectacular performance in Germany in the second leg. Post-match, Martin O'Neill said, "Anybody who thinks that's a good idea needs their head examining. There's no question about it. It sends out totally the wrong message. We are playing against Stuttgart. The game is hard enough."

Stuttgart took the lead 15 minutes into the game, thanks to Bilal El-Khannouss. Six minutes later, Celtic levelled through Benjamin Nygren, but El-Khannouss put his side back in front in the 28th minute.

From that point on, Stuttgart led in the game and built on their advantage. Jamie Leweling made it 3-1 in the 57th minute, before Tiago Tomás added his team's fourth in added time.

Celtic need to produce a perfect performance to give themselves a chance of reaching the competition's round of 16 away from home.

22 years ago was the last time Celtic won a European knockout game, which was against Barcelona, and O'Neill was the manager at the time.

There are clear problems for Celtic off the pitch, which are impacting the club's on-field performances. What do you think is the single biggest problem at Celtic right now?