Rangers manager Walter Smith will not field a weakened team against Sporting Lisbon despite a crucial league meeting with Celtic looming on Sunday.Rangers host the Portuguese in the last 32 of the Europa League on Thursday before taking on their Glasgow rivals. [LNB]"It's an important game on Sunday but this one is an important game too," said Smith. [LNB]"We don't enter tournaments to lose them. We want to do as well as we possibly can." [LNB]Rangers are battling on four fronts for silverware and Smith refused to prioritise the competitions his side are involved in. [LNB]"We didn't start out in the Europa League, we started out in the Champions League and were unable to stay in the Champions League," he added. "We are in the Europa League and we want to do as well as we can. [LNB]"Someone asked me if we take the League Cup in Scotland seriously. [LNB]"We have been in every final since I came back so I just replied that they should ask everybody else if they take it seriously. We take all the games we have seriously. [LNB]"I don't think you can pick and choose what you wish to be successful in. You want to do well in every game you play and every tournament you play in." [LNB]Rangers found themselves in a similar situation the last time they met Sporting en-route to the Uefa Cup final in 2008, when a packed schedule culminated in missing out on both the European trophy and the Scottish Premier League title. [LNB]But Smith added: "It's dead simple just now. You've got to win your games.[LNB]Rangers will be up against former favourite Pedro Mendes"If we put out a far weakened team or a reserve team and they lost the game and then we put out our strongest team and we lose on Sunday, we have lost two games. [LNB]"You've got to try and win your games. It's a silly circumstance for everybody to say you are involved in professional football and you don't want to win a game. [LNB]"We've got to try to win the matches we play." [LNB]Celtic, who have home advantage at the weekend, lead the SPL by four points but Rangers have two games in hand. [LNB]While the Scottish title race is close, Sporting trail leaders Porto by 23 points in their own domestic competition. [LNB]However, Smith remains wary of Thursday's opponents, saying: "They have good players. Despite the fact they may have problems personnel-wise and financially at their club overall, they still have good players in their team. [LNB]"They managed to get to this stage of the Europa League. [LNB]"Their domestic form may not be the best and it doesn't look as though they will challenge for the championship, so they may see the Europa League as an opportunity to get them a bit of credibility back. [LNB]"We know Pedro Mendes extremely well obviously, [Helder] Postiga has a goalscoring capability. [LNB]"They have good players in their team and we are not in a position where we can look at any team and say we don't have to treat them with the utmost respect."