Louis van Gaal
Van Gaal's young side sealed another league win against Watford on Wednesday.Getty

Louis van Gaal admits his Manchester United side still have a tough road ahead of them with many of his players lacking match fitness, despite extending their winning run to four games.

Juan Mata's late free-kick sealed a 1-0 win over Watford on 2 March at Old Trafford, securing United's first back-to-back wins in the league since November 2015. With Manchester City losing to Liverpool on the same night, the race for fourth spot is now back on, with United now sat level on points with their neighbours.

That winning run has been put together amid another injury crisis at the club with van Gaal turning to the club's youngsters to fill the void, with five members of the Under-21 squad making their first-team debuts in recent weeks.

But with Chris Smalling, Wayne Rooney and Bastian Schweinsteiger among an 11-man injury list, van Gaal has urged caution over the club's return to form.

"We are fighting and we are struggling but, in the struggle, we can play fantastic matches," Van Gaal said. "We have to go step by step. We have four wins in a row, fantastic, but we have a very small selection of players at the moment. When players are coming back, they are not fit enough. You saw how [Marcos] Rojo is struggling.

With United battling on three fronts, Van Gaal's depleted squad face the possibility of 18 more games before the season is out – if they are to reach the finals of the FA Cup and the Europa League.

"You can see the statistics, how many players are injured and from what date, then you can see how difficult it was. We are still in with the possibility of being in the top four of the league and I don't think that's bad — and we're in the quarter-finals of the FA Cup and last 16 of the Europa League. But it also means it's a full programme."