Sir Alex Ferguson has stated that Phil Jones's participation in the England Under-21 team at this summer's European Championship is not guaranteed as Manchester United continue to monitor his return from injury.

Earlier this week Roy Hodgson, the England manager, said Jones should be part of a strong squad for Stuart Pearce, the Under-21s' head coach. Ferguson, however, did not sound so sure. "We'll have to wait and see how things are," he said. "The boy's had an injury this season, which has needed looking after. We'll see what it's like in the summer."

Jones missed the start of the season because of a back problem before suffering a more serious knee injury that meant he did not play his first game of the campaign until 20 November.

Jones was a member of Hodgson's senior squad at last summer's European Championship and Ferguson is bemused that he will play for Pearce's team in Tuesday's match against Sweden at Walsall. "I haven't paid much attention to it but I'm surprised he's in the Under-21s and not the full squad," said Ferguson.

"It's happened quite a few times to players [to drop down into the Under-21s] and it's understandable. But for the players that's more difficult to manage because once a player gets into a full squad he thinks he's achieved what he wants to achieve and taking the step back can be hard to manage. But he's 20 and maybe he's as good as the Under-21 squad are going to get."

Although United lead the Premier League scoring charts with 59 goals, – 10 more than the next most prolific side, Chelsea – Ferguson is concerned that his side has not scored more and been more ruthless.

On Wednesday at Old Trafford they hung on to beat Southampton 2-1 after they endured a second-half onslaught from the visitors and Ferguson admitted: "It only takes a second to lose a goal and that second half against Southampton was another reminder.

But we dug in and bringing [Rio] Ferdinand on at that vital time [on 63 minutes], his experience helped us a little bit. We blocked shots, [Nemanja] Vidic got three or four important headers. We sorted it out. In my experience, there are always one or two games a season where you say to yourself: 'we were lucky today.' I think we were lucky in the second half.

"It must be hard for our fans. It was poor from us. We should have been 5-0 up at half-time. That's happened a few times this season – we've been in comfortable positions but haven't dug our nails into it.

"It's frustrating because I know we're capable of doing that. It could go to goal difference [like last season's title] and that's an issue. At the moment we're only two goals better off than Manchester City. That could be undone in one game. We've had opportunities to be better."

Southampton scored after only two minutes following a mix-up between Michael Carrick and David de Gea. Of the goalkeeper, Ferguson said: "He was caught in-between things. He was in no man's land. Michael Carrick was great with it. He knew it was a bad pass back and we move on. I think it's refreshing when players put their hand up and acknowledge their mistakes. You don't get many players doing that in the modern-day game. If you go back to the days of [Bryan] Robson and [Steve] Bruce, they'd always put their hand up. They were that type of character. But we handled it well and played well after that. It didn't take us long to get the equaliser and by half-time we should have been 4-0 or 5-0 up."

United would be 10 points ahead of City if they beat Fulham on Saturday as the champions host Liverpool on Sunday. But Ferguson said: "I don't think we can afford to drop any – when you drop points it only encourages everybody around you. The important thing is to win the league. I don't care what the total is. I think our attitude is right, our concentration has been good.

"I know fine well that points will be dropped, I suppose, by both ourselves and Manchester City. But I'm not looking to pre-empt things. I hope we don't drop points, particularly in the next few games. But it happens and you have to deal with it."

Ferguson has denied a charge of misconduct in relation to his comments about the assistant referee Simon Beck following the 1-1 draw with Tottenham Hotspur last month in which he allegedly "implied that the match official was motivated by bias". Ferguson has requested a paper [personal] hearing and a date is yet to be set.