Efe Ambrose welcomes the challenge to Celtic's Scottish Premiership title hopes this season but thinks the best has yet to come from the Glasgow side.
Aberdeen have overtaken the reigning champions at the top of the table.
"Aberdeen are at the top and they deserve it, they are a great team and have been playing well," said the Nigeria defender.
"We respect them and we look for the challenge from them. Not just them, Dundee United, so we need to step up."
The Dons leapfrogged Celtic with a 2-0 New Year's Day win over St Johnstone before Celtic's match away to Partick Thistle was postponed because of a waterlogged pitch.
Only five points separate the top five sides, with United, Hamilton Academical and Inverness Caledonian Thistle also within touching distance.
But, despite his side having lost as many points before the new year as they did in the whole of last season, Ambrose believes any possible threat to their title will simply spur on the Celtic squad.
"The best of Celtic is going to come because we know there are teams behind us trying to take the title from us," he added.
"What we need to do is win every game from now until the end of the season and I believe we have the ability and the squad that can do that.
"But it is easier said than done. People think it is easy for Celtic to win the league, but it isn't.
"Every team wants to beat Celtic, so that makes it difficult. It puts pressure on us and it is not easy.
"We have to have the character. We have not been at our best, but that is football."