Celtic were knocked out of the Europa League by Inter Milan on Thursday.
John Hartson has urged the Celtic players to bounce back from their exit from the Europa League.
The defending Scottish champions went down 1-0 to Inter Milan away from home in the second leg of the round-of-32 tie on Thursday.
The result at the San Siro meant that Celtic lost the tie 4-3 on aggregate and relinquished their chances of winning the Europa League.
Former Celtic striker Hartson was disappointed to see Ronny Deila’s side crash out of the European competition.
However, the ex-Wales international was pleased with the performance of the 10-man Celtic team in Italy and has urged them to pick themselves up.
Excellent effort from the Hoops. Very harsh sending off.. That's the quadruple gone!! Treble still in sight.. Dust themselves down go again.— John Hartson (@JohnHartson10) February 26, 2015
Celtic will return to action on Sunday when they take on second-placed Aberdeen at Celtic Park in the Scottish Premiership.
The Bhoys are currently three points clear at the top of the league table, having played a fewer game than Aberdeen.
Despite their Europa League disappointment, Celtic are very much in contention of winning the treble.
The Glasgow-based outfit are favourites to win the Premiership title, have reached the quarter-finals of the Scottish Cup, and will face Dundee United in the final of the Scottish League Cup.