Blackburn Rovers v Manchester United:  Alex Ferguson has new signing Patrice Evra available for tonight's semi-final at Blackburn.

The French international completed his Manchester United medical without a hitch earlier yesterday, so the £5million arrival from Monaco will go straight into Ferguson's squad for the Ewood Park clash.

Ferguson is expected to make wholesale changes to the side that drew at Burton Albion on Sunday, but Park Ji-sung (knee) is almost certainly out and United's other transfer window arrival, Nemanja Vidic, will not be considered due to a lack of match fitness.

Ferguson is ready to take a risk tonight so as to ensure his side are fully primed for their derby-day trip to the City of Manchester Stadium. United have a lunchtime engagement with Stuart Pearce's side on Saturday when local pride is on the line as well as a chance to cut Chelsea's Premiership lead to 10 points.

So, although his side could take a massive step towards next month's League Cup final at the Millennium Stadium by winning at Ewood Park, Ferguson is prepared to field a below-strength side for the first leg encounter in order to keep some of his key men fresh for the weekend test.

"Blackburn will play their strongest side tomorrow, but we won't," Ferguson said yesterday. "I will make changes from the FA Cup game at Burton because I have to look at the City match on Saturday.

"That is the whole point in having a squad. We have the numbers now to adapt to the fact we are playing away from home, then we will see what position we are in for the second leg."

Whether Ferguson's side is as weak as he is suggesting remains to be seen. Of the side that started Sunday's goalless draw at Burton, only Mikael Silvestre and Wes Brown would be regarded as first choice and the arrival of Evra is expected to nudge one of them out of Ferguson's line-up.

If he does go through with his threat, Ferguson's strategy is a major gamble given United are already out of the Champions League and have next to no chance of overhauling Chelsea in the league title race.

Yet, he adopted a similar attitude to what was expected to be a tricky quarter-final tie at Birmingham before Christmas and came away from St Andrews with a comfortable win.

United defeated Blackburn at the same stage of the competition three seasons ago, but their recent record against Rovers is not good. They have not scored a victory over Rovers in four attempts - Mark Hughes is unbeaten in two outings against his former club since replacing Graeme Souness as manager and Rovers have already beaten United at Old Trafford this season, Morten Gamst Pedersen scoring both goals in a surprise 2-1 win last September.

Pedersen himself believes it will be no fun beating United unless Ferguson fields his strongest line-up. The Norway international is adamant September's result was no fluke and can be repeated in both legs of their semi-final clash.

Hughes looks set to field his first-choice line-up and, Pedersen is hoping Ferguson wheels out his big guns.

"I watched some of the game with Burton," said Pedersen, who grew up a United fan. "I was surprised at the result, but it shows if you are not on top of your game then anything can happen. We know it will be a different United side tomorrow - I hope so. It will be more fun if we beat their best team.

"But we know what we have to do to beat them. If we do, then we know we are a really good side. Having beaten them before at Old Trafford, we know we can do it again.

"As a player it's good to have in your mind that you've beaten them before. That helps, but it's still not going to be easy."

Hughes has a fully-fit squad to choose from, with Republic of Ireland midfielder Steven Reid available again after serving a one-match ban.

Ewood Park, 8pm/On TV: Sky Sports 1