Madjid Bougherra has backed recent Rangers signing El Hadji Diouf to brush off any verbal onslought from home fans at Celtic Park on Sunday.Diouf infamously spat at Celtic supporters while playing for Liverpool in the 2003 Uefa Cup quarter-final. [LNB]He was also the subject of a face-to-face goal celebration from Celtic captain Scott Brown in February. [LNB]"You see him in the last game," said defender Bougherra. "He is very professional and did not react." [LNB]The spitting incident was only one of several controversial moments during a career in English football that led to the questioning of Diouf's temperament. [LNB]But Bougherra expects the Senegal forward to make a positive contribution to a Scottish Premier League match on Sunday that could go a long way to deciding which of the two Glasgow clubs win the title. [LNB]"He played in Africa and in Senegal, where the pressure on the team is more than this," said Rangers' Algeria defender.[LNB] We know we have to go there and turn in as good a performance as we are going to do in the league championship all season Rangers manager Walter Smith "Off the pitch, he is a fantastic guy - he is funny, he is cool, he is a very nice guy. [LNB]"On the pitch, he is different. He wants to win and likes to battle, but you have to respect that. [LNB]"But, at the moment, we are very happy with him and he is very quiet and professional. Every guy in the team likes him." [LNB]Reigning champions Rangers go into game five points adrift of Celtic but having played two fewer games. [LNB]"We have some games in hand, but we need to win this game or a minimum of a draw to retain the gap because Celtic are in good form and are a good team," said Bougherra. [LNB]"We go there to win, but if we come back with a draw, we have got to be happy. [LNB]"The championship is going to be very hard this season, because we have Hearts behind us and Celtic are likely to win every other game, so this season is more tough than last season." [LNB]Rangers make the short trip across Glasgow three days after a testing 1-1 draw at home to Sporting in the Europa League, while Celtic had no midweek fixture, leading to suggestions that the visitors could suffer from tiredness.[LNB]Brown aimed his Ibrox goal celebration at Diouf"Physically, yes, mentally no," said Bougherra. "You need consistency and sometimes it is not easy when you have many games, like Europa League, because it takes some energy, but we have two days to recover. [LNB]"But every Celtic game is special because we have a good atmosphere, so the confidence and motivation is there." [LNB]Rangers manager Walter Smith stopped just short of saying that Sunday's result would go a long way to deciding the destiny of the title. [LNB]"It's obviously an important game in terms of the championship overall," he said. [LNB]"We've already lost three games in the league this season and we don't want to be losing many more. [LNB]"We know we have to go there and turn in as good a performance as we are going to do in the league championship all season." [LNB]Rangers won the first Old Firm game of the season 3-1 at Celtic Park, but their rivals dominated the next two encounters, winning 2-0 at Ibrox in the SPL before Brown's equaliser ensured a 2-2 draw at the same venue in the Scottish Cup. [LNB]Smith also has a smaller squad at his disposal with which to cope with the backlog of fixtures but backs his side to overcome those problems. [LNB]"We have had Champions League games and we had to put up with that," he added. "Celtic have the obvious advantage of not having European matches, if it is an advantage. [LNB]"It certainly allows them a freshness that we will be lacking. [LNB]"But our own group have shown a good determination and will to win and hopefully that will counteract any tiredness we might feel."