Joey O'Brien has warned his players - and Shels supporters - to expect Rijeka to be fired up by talisman Toni Fruk's return for tomorrow night's European qualifier at Tolka Park (7.45pm).An attacking midfielder, capped at every international age-group from u14 to u21 (eight age-groups!), he was called into the world-ranked 10th Croatia squad for their two World Cup qualifiers in June.Fruk wears no10 and has already been written in as the successor to current no10 Luca Modric, 39, who is expected to retire either in or just after this World Cup cycle. READ MORE: Heimir Hallgrimsson will be thrilled with Troy Parrott’s comments as Ireland striker’s sensational scoring run continues READ MORE: Ciara Mageean receives support on Camogie's big day at Croke Park “As you might expect, playing at the level they play at, Rijeka are serious opposition and have serious quality players," warns shels boss Joey O'Brien.“Their main man Toni Fruk was suspended in the first leg but from watching the videos of previous games, and he played against Ludogorets in both games, he was probably one of the best players on the pitch."He started their league game at the weekend and he’ll come straight back in and add a different dimension to them because he’s a top, top player so we’ll be on guard."Shels, 2-1 to the good from the first leg of their Uefa Europa League, 3rd qualifying round, will be specifically looking to close down the space on the flanks."I suppose people probably haven’t seen how good a team they were, I don’t know how many people seen the match but we are going to be up against it. "In possession, they are really good, they use wingers on the side of the pitch, one-v-ones, we had our hands full there and we know that."It’s going to be a tough, tough night but as I’ve always said, we’re playing here at Tolka, they’ve no fans so it’s going to be a full house all for us, so we are going out to win."It’s going to be a great challenge for us and one we can’t wait for, it is very exciting."There was a capacity 5,474 at Tolka on Saturday evening for the Bohs derby and the Rijeka match is also sold out with the Shels boss adding:"I thought the atmosphere here today from both sets of fans was brilliant and, as a game of football showcased our league, a full house."I just said to someone over there that I don’t think ten years ago with a game like Leeds and AC Milan across the road, I don’t think this place would have been full."So I think it shows where our league is at, overall, I’m sure both sets of fans, they got their money’s worth today.Striker Seán Boyd is not expected to return from the calf injury that has been dragging on longer than hoped although there was some consolation in a lively display from new signing Sean Moore. “Seán looks to be struggling and I don’t think he’ll turn it around that quick."And I don’t think there were too many injuries tonight (against Bohs), we were able to get more minutes into the lads who haven’t been starting, they’ve got a start, I’m sure they’re raring to go for Tuesday."Seán Moore coming in as a new player starting after a couple of pre-season games, he needs to get going, I wanted to see him, coming off that side of the pitch onto his left foot. thought in the first half he opened up a couple of moments. He’ll only get better." Get the latest sports headlines straight to your inbox by signing up for free email alerts.