The local rivals find themselves level on points with only two games to play after City claimed a 1-0 on Monday night over their neighbours thanks to a Vincent Kompany header.
Sunday sees Roberto Mancini’s men travel to Newcastle before United host Swansea at Old Trafford and Sir Alex feels that City won’t find it easy against Alan Pardew’s following their win at Chelsea on Wednesday.
"Newcastle is a very difficult place and they are playing well,” Sir Alex told reporters.
|13/8||Manchester United are now 13/8 with bet365 to win the Premier League this year.|
"After that incredible defeat at Wigan, they galvanised themselves to win at Chelsea and, as everyone knows, winning at Chelsea is very difficult. We have not done it for eight years."
City currently occupy top spot on goal difference - leading United by eight goals - and Sir Alex does not think his side will be able to overtake them if they win their remaining two fixtures.
"They have got two games left. If they win their two games they win the league," he said.
"People talk about goal difference, but it depends how many they win by. Say they win 3-0 on Sunday, their lead would be 11 and they still have QPR at home.
"That would be impossible."